Extraneuronal cholinergic system in lymphocytes

In vivo release of non-neuronal acetylcholine from human skin by dermal microdialysis: effects of sunlight, UV-A and tactile stimulus

Non-neuronal acetylcholine (ACh) is expressed in epithelial, endothelial and immune cells. For example, the in vivo release of ACh from the human skin pretreated with botulinum toxin has recently been demonstrated. In the present experiments the effects of light (sunlight and solar radiation by a commercial UV-A applier) and of a tactile stimulus on the release of non-neuronal ACh were investigated. Release of ACh from the proximal and distal shin, i.e. anterior tibial region, was measured by dermal microdialysis in 20 min samples over a time period of at least 140 min. Control experiments were performed in a dark room throughout. In some experiments volunteers were exposed to sunshine (80-140 min) or the shin region was illuminated (80-95 min) by a commercial UV-A lamp (400 W at a distance of 50 cm). In control experiments ACh release between 20 and 80 min (B1) amounted to 118+/-32 pmol (n=17) and gradually declined between 80 and 140 min (B2) to 112+/-34 pmol, resulting in a B2/B1 ratio of 0.95. When the skin was exposed to sunlight ACh release increased from 205+/-58 pmol (B1) to 349+/-122 pmol resulting in a B2/B1 ratio of 1.70. UV-A radiation, however, had no significant effect on the B2/B1 ratio. When very smooth tactile stimuli were applied by a cotton wool tip for 20 min to the skin close to the microdialysis membranes in a dark room, ACh release was increased from 9+/-2 pmol/20 min to 52+/-36 (n=7). In conclusion, the in vivo release of ACh from the human skin appears to be regulated by external stimuli like sunlight and tactile stimuli.

Release of non-neuronal acetylcholine from the isolated human placenta is affected by antidepressants

Non-neuronal acetylcholine (ACh) is released from the human placenta into the extracellular space via organic cation transporters (OCTs). The present experiments investigated whether ACh release from epithelial cells is affected by drugs which are substrates of OCTs. The antidepressant drugs amitriptyline and doxepine were tested as both substances are not approved for pregnant women but frequently used. Release of ACh was measured in 10 min intervals over a period of 100 min. Test substances were added from t=50 min of incubation onwards. The effect was calculated by comparing the ACh release of the last three samples (t=70-100 min; B2) with that immediately before the application of the test substances (t=20-50 min; B1). The baseline ACh release amounted to 2.07+/-0.17 nmol/10 min (n=29; villus). Under control conditions a B2/B1 ratio of 0.78+/-0.02 was obtained. The following B2/B1 ratios were found, when therapeutic drugs were added: 0.54+/-0.04 (n=7; P<0.05) in the presence of 10 microM amitriptyline; 0.44+/-0.04 (10; P<0.01) in the presence of 10 microM doxepin; 0.73+/-0.04 (13) in the presence of 10 microM metformin; 0.76+/-0.06 (7) in the presence of 10 microM minoxidil; 0.63+/-0.03 (10) in the presence of 1 microM theophylline. The results demonstrate that antidepressants reduce the release of non-neuronal ACh at least in the human placenta, most likely by intracellular substrate competition at the polyspecific organic cation transporters (OCTs) but only at concentrations roughly 30-fold above the therapeutic range. Theophylline may also interfere with the release of non-neuronal ACh.

Muscarinic acetylcholine receptor activation increases transcellular transport of macromolecules across mouse and human intestinal epithelium in vitro

The intestinal epithelium acts as a barrier restricting uptake of luminal macromolecules such as dietary antigens and microbes. Here, we examined the role of cholinergic signalling in the regulation of permeability to macromolecules. Mouse jejunum was mounted in Ussing chambers and permeability was determined by measuring the flux of the antigen-sized protein, horseradish peroxidase (HRP), across the tissue. Baseline HRP permeability was significantly reduced by neural blockade with tetrodotoxin or cholinergic muscarinic antagonism with atropine, suggesting that ongoing release of endogenous acetylcholine from enteric nerves regulates barrier function. Exogenous addition of the muscarinic agonist bethanechol caused significant increases in both HRP flux and the area of HRP-containing endosomes in enterocytes. Bethanechol-enhanced HRP flux was abrogated by the M3 receptor antagonist, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), the phospholipase A(2) inhibitor quinacrine, and the cyclooxygenase inhibitor indomethacin. Complementary in vitro studies showed direct effects of bethanechol on T84 epithelial cells, where increased HRP uptake was associated with increased F-actin, and increased cytosolic phospholipase A(2) (cPLA(2)) phosphorylation. Taken together, these results provide evidence for cholinergic regulation of transepithelial transport of macromolecules, mainly mediated by activation of M3 receptors with subsequent involvement of phospholipase A(2) and cyclooxygenase products.

Nicotine and serotonin in immune regulation and inflammatory processes: a perspective

Nicotine and serotonin modulate the innate and adaptive immune responses and the inflammatory states. Several nicotinic cholinergic and serotonergic receptor subtypes have been characterized in B and T lymphocytes, monocytes, macrophages, and dendritic cells. The use of knockout mice has allowed a better characterization of nicotinic receptors and their role in anti-inflammatory processes in these cells. Cytokines play a crucial role in controlling inflammatory reactions. Nicotine and serotonin have been reported to regulate cytokine release. Cholinergic mechanisms also play an important role in inflammation through endogenous acetylcholine. Nicotine mimics this effect by activating the cholinergic anti-inflammatory pathways. New concepts of reciprocal interactions between nicotine and serotonin are emerging. The role of nicotine as an anti-inflammatory agent has been established, whereas that of serotonin remains more controversial.

Simvastatin regulates non-neuronal cholinergic activity in T lymphocytes via CD11a-mediated pathways

Lymphocyte function associated antigen-1 (LFA-1; CD11a/CD18) is an important mediator of leukocyte migration and T cell activation. We previously showed that antithymocyte globulin stimulates an independent, non-neuronal cholinergic system in T cells via LFA-1-mediated pathways, as evidenced by increases in acetylcholine (ACh) synthesis and choline acetyltransferase (ChAT) mRNA expression. The cholesterol-lowering drug simvastatin inhibits LFA-1 signaling by binding to an allosteric site on CD11a (LFA-1 alpha chain), which leads to immunomodulation. In the present study, we investigated whether simvastatin modulates lymphocytic cholinergic activity in T cells. We found that anti-CD11a monoclonal antibody (mAb) increased ChAT activity, ACh synthesis and release, and expression of ChAT and M5 muscarinic ACh receptor mRNA in MOLT-3 cells, a human leukemic T cell line. Simvastatin abolished these anti-CD11a mAb-induced increases in lymphocytic cholinergic activity in a manner independent of its cholesterol-lowering activity. These results indicate that LFA-1 contributes to the regulation of lymphocytic cholinergic activity via CD11a-mediated pathways, and suggest that simvastatin exerts its immunosuppressive effects in part via modification of lymphocytic cholinergic activity.

Cholinergic regulation of epithelial ion transport in the mammalian intestine

Acetylcholine (ACh) is critical in controlling epithelial ion transport and hence water movements for gut hydration. Here we review the mechanism of cholinergic control of epithelial ion transport across the mammalian intestine. The cholinergic nervous system affects basal ion flux and can evoke increased active ion transport events. Most studies rely on measuring increases in short-circuit current (ISC = active ion transport) evoked by adding ACh or cholinomimetics to intestinal tissue mounted in Ussing chambers. Despite subtle species and gut regional differences, most data indicate that, under normal circumstances, the effect of ACh on intestinal ion transport is mainly an increase in Cl- secretion due to interaction with epithelial M3 muscarinic ACh receptors (mAChRs) and, to a lesser extent, neuronal M1 mAChRs; however, AChR pharmacology has been plagued by a lack of good receptor subtype-selective compounds. Mice lacking M3 mAChRs display intact cholinergically-mediated intestinal ion transport, suggesting a possible compensatory mechanism. Inflamed tissues often display perturbations in the enteric cholinergic system and reduced intestinal ion transport responses to cholinomimetics. The mechanism(s) underlying this hyporesponsiveness are not fully defined. Inflammation-evoked loss of mAChR-mediated control of epithelial ion transport in the mouse reveals a role for neuronal nicotinic AChRs, representing a hitherto unappreciated braking system to limit ACh-evoked Cl- secretion. We suggest that: i) pharmacological analyses should be supported by the use of more selective compounds and supplemented with molecular biology techniques targeting specific ACh receptors and signalling molecules, and ii) assessment of ion transport in normal tissue must be complemented with investigations of tissues from patients or animals with intestinal disease to reveal control mechanisms that may go undetected by focusing on healthy tissue only.

Development of methods to measure humoral immune responses against selected antigens in the common marmoset (Callithrix jacchus) and the effect of pyridostigmine bromide administration

This methodological study was carried out in preparation for a major long term study, also reported in this volume, which was designed to investigate whether the combination of vaccines and pyridostigmine bromide (PB) could have been responsible for adverse signs and symptoms reported by a number of veterans of the 1990/1991 Gulf conflict. In this context, the marmoset has been used to model aspects of the human immune system. The purposes of this methodological study were to select appropriate immunochemical reagents to measure humoral responses induced in marmosets in response to selected health and hygiene and biological warfare vaccines and to initially assess the effects of PB on the responses recorded. Vaccines were administered at 1/5th of a human dose, and also investigated in combination with the nerve agent pretreatment compound PB. PB dosing was selected to induce an inhibition of erythrocyte acetylcholinesterase by 30%. In order to assess the functionality of the immune system, antibody responses to a neo-antigen (keyhole limpet haemocyanin--KLH), administered some 2 months following the completion of the vaccination schedule, were measured. The present study identified appropriate isotyping reporter reagents which cross-reacted with equivalent marmoset immunoglobulins. Robust antibody responses were identified against anthrax protective antigen (PA), whole cell pertussis vaccine and KLH, while weaker responses were measured against cholera and typhoid vaccines. The killed whole cell plague vaccine induced a response which was at the limit of detection of the assay. Coadministered PB had no discernable effect on immunological responses in this study.

Ethidium bromide inhibits rat brain acetylcholinesterase activity in vitro

Ethidium bromide (EtBr), a fluorescent dark red compound and stain for double-stranded DNA and RNA was used to study acetylcholinesterase (AChE) activity in vitro together with kinetic parameters of this enzyme in the striatum (ST), hippocampus (HP), cerebral cortex (CC) and cerebellum (CB) of adult rats. AChE activity in vitro in the ST, HP, CC and CB was significantly reduced (p<0.05) in the presence of EtBr at concentrations of 0.00625, 0.0125, 0.025, 0.05 and 0.1 mM. For the analysis of the kinetic three concentrations of EtBr were tested (0.00625, 0.025 and 0.1 mM). An uncompetitive inhibition type was observed in the ST, HP and CC, whereas in the CB the inhibition type was mixed. These data indicate that EtBr should be considered a strong inhibitor of AChE activity demonstrating that there is an interaction between this compound and the cholinergic system.

Acetylcholinesterase Activity in Rats Experimentally Demyelinated with Ethidium Bromide and Treated with Interferon Beta

The ethidium bromide (EB) demyelinating model was associated with interferon beta (IFN-beta) to evaluate acetylcholinesterase (AChE) activity in the striatum (ST), hippocampus (HP), cerebral cortex (CC), cerebellum (CB), hypothalamus (HY), pons (PN) and synaptosomes from the CC. Rats were divided into four groups: I control (saline), II (IFN-beta), III (EB) and IV (EB and IFN-beta). After 7, 15 and 30 days rats (n = 6) were sacrificed, and the brain structures were removed for enzymatic assay. AChE activity was found to vary in all the brain structures in accordance with the day studied (7-15-30 days) (P < 0.05). In the group III, there was an inhibition of the AChE activity in the ST, CB, HY, HP and also in synaptosomes of the CC (P < 0.05). It was observed that IFN-beta per se was capable to significantly inhibit (P < 0.05) AChE activity in the ST, HP, HY and synaptosomes of the CC. Our results suggest that one of the mechanisms of action of IFN-beta is through the inhibition of AChE activity, and EB could be considered an inhibitor of AChE activity by interfering with cholinergic neurotransmission in the different brain regions.

Intravenous administration of choline or cdp-choline improves platelet count and platelet closure times in endotoxin-treated dogs

This study was performed to assess the effects of intravenous choline chloride and cytidine-5'-diphosphate choline (CDP-choline) treatments on circulating platelet, white blood cell, and red blood cell counts and platelet functions in response to endotoxin. Saline (0.2 mL/kg), choline chloride (20 mg/kg), or CDP-choline (70 mg/kg) were given intravenously three times at 4-h intervals, and endotoxemia was induced by endotoxin (E. coli 055:B5, 20 microg/kg) infusion, 5 min after the first treatment. Blood samples were collected before and at multiple time points after the challenge, for a panel of hematologic parameters and platelet closure times measured by PFA-100. In saline-treated dogs, circulating platelet counts decreased by 85% (P < 0.001) at 0.5 h and remained low by 36%-80% (P < 0.5-0.001) 1-12 h after endotoxin. Circulating WBC counts decreased by 80%-90% (P < 0.001) at 0.5-2 h, and increased (P < 0.001) by 190% 12 h after the endotoxin. In response to endotoxin, RBCs increased by 10%-13% (P < 0.05) at 1-12 h. Endotoxin-induced decline in circulating platelets was attenuated at 0.5 h (P < 0.05-0.01) and reversed at 1-12 h (P < 0.05-0.001) by choline. Platelet closure times were shortened from 81 +/- 10 s and 135 +/- 10 s to 29 +/- 5 s (P < 0.001) and 60 +/- 3 s (P < 0.001) at 0.5 h, and prolonged (P < 0.001) at 1-8 h after endotoxin induction. Endotoxin-induced shortening in platelet closure times was attenuated (P < 0.05) and blocked (P < 0.01) by choline and CDP-choline, respectively. These results showed that choline and CDP-choline treatments improved circulating platelet counts and platelet function during endotoxemia in dogs.

Muscarinic receptor signaling in the pathophysiology of asthma and COPD

Anticholinergics are widely used for the treatment of COPD, and to a lesser extent for asthma. Primarily used as bronchodilators, they reverse the action of vagally derived acetylcholine on airway smooth muscle contraction. Recent novel studies suggest that the effects of anticholinergics likely extend far beyond inducing bronchodilation, as the novel anticholinergic drug tiotropium bromide can effectively inhibit accelerated decline of lung function in COPD patients. Vagal tone is increased in airway inflammation associated with asthma and COPD; this results from exaggerated acetylcholine release and enhanced expression of downstream signaling components in airway smooth muscle. Vagally derived acetylcholine also regulates mucus production in the airways. A number of recent research papers also indicate that acetylcholine, acting through muscarinic receptors, may in part regulate pathological changes associated with airway remodeling. Muscarinic receptor signalling regulates airway smooth muscle thickening and differentiation, both in vitro and in vivo. Furthermore, acetylcholine and its synthesizing enzyme, choline acetyl transferase (ChAT), are ubiquitously expressed throughout the airways. Most notably epithelial cells and inflammatory cells generate acetylcholine, and express functional muscarinic receptors. Interestingly, recent work indicates the expression and function of muscarinic receptors on neutrophils is increased in COPD. Considering the potential broad role for endogenous acetylcholine in airway biology, this review summarizes established and novel aspects of muscarinic receptor signaling in relation to the pathophysiology and treatment of asthma and COPD.

Stress-induced cholinergic signaling promotes inflammation-associated thrombopoiesis

To study the role of the stress-induced “readthrough” acetylcholinesterase splice variant, AChE-R, in thrombopoiesis, we used transgenic mice overexpressing human AChE-R (TgR). Increased AChE hydrolytic activity in the peripheral blood of TgR mice was associated with increased thrombopoietin levels and platelet counts. Bone marrow (BM) progenitor cells from TgR mice presented an elevated capacity to produce mixed (GEMM) and megakaryocyte (Mk) colonies, which showed intensified labeling of AChE-R and its interacting proteins RACK1 and PKC. When injected with bacterial lipopolysaccharide (LPS), parent strain FVB/N mice, but not TgR mice, showed reduced platelet counts. Therefore, we primed human CD34+ cells with the synthetic ARP26 peptide, derived from the cleavable C-terminus of AChE-R prior to transplantation, into sublethally irradiated NOD/SCID mice. Engraftment of human cells (both CD45+ and CD41+ Mk) was significantly increased in mice that received ARP26-primed CD34+ human cells versus mice that received fresh nonprimed CD34+ human cells. Moreover, ARP26 induced polyploidization and proplatelet shedding in human MEG-01 promegakaryotic cells, and human platelet engraftment increased following ex vivo expansion of ARP26-treated CD34+ cells as compared to cells expanded with thrombopoietin and stem cell factor. Our findings implicate AChE-R in thrombopoietic recovery, suggesting new therapeutic modalities for supporting platelet production.

The acetylcholinesterase inhibitor, Donepezil, regulates a Th2 bias in Alzheimer's disease patients

The increased pro-inflammatory cytokine production was previously observed in Alzheimer's disease (AD). We sought to explore whether acetylcholinesterase inhibitor (AChEI) therapy ameliorates clinical symptoms in AD through down-regulation of inflammation. Expression and release of monocyte chemotactic protein-1 (MCP-1), a positive regulator of Th2 differentiation, and interleukin (IL)-4, an anti-inflammatory cytokine from peripheral blood mononuclear cells (PBMC) in AD patients, were investigated. PBMC were purified from AD patients at time of enrollment (T0) and after 1 month of treatment with AChEI (T1) and from healthy controls (HC). Supernatants were analyzed for cytokine levels by ELISA methods. mRNA expression were determined by RT-PCR. Expression and production of MCP-1 and IL-4 were significantly increased in AD subjects under therapy with the AChEI Donepezil, compared to the same AD patients at time of enrollment (P < 0.001). Our data suggest another possible explanation for the ability of Donepezil [diethyl(3,5-di-ter-butyl-4-hydroxybenzyl)phosphonate] to delay the progression of AD; in fact, Donepezil may modulate MCP-1 and IL-4 production, which may reflect a general shift towards type Th0/Th2 cytokines which could be protective in AD disease. The different amounts of MCP-1 and IL-4 observed might reflect the different states of activation and/or responsiveness of PBMC, that in AD patients could be kept in an activated state by pro-inflammatory cytokines.

Expression and production of two selected beta-chemokines in peripheral blood mononuclear cells from patients with Alzheimer's disease

MCP-1 and RANTES are molecules that regulate monocyte and T-lymphocyte recruitment towards sites of inflammation. We sought to evaluate the role of these chemokines in Alzheimer's disease (AD), and the effect of acetylcholinesterase inhibitor (AchEI) therapy on their release from peripheral blood mononuclear cells (PBMC). MCP-1 and RANTES mRNA expressions were determined by RT-PCR and the amount of secreted chemokines was assayed using specific ELISA methods from purified PBMC from each AD patients (n = 40) at the time of enrolment (T0) and after 1 month of treatment with AchEI (T1) and from 20 healthy age and sex-matched subjects (HC). We found that expression and production of MCP-1 in AD patients was significantly lower than in HC subjects. After 1 month of therapy with AchEI (Donepezil), MCP-1 levels increased in each patient. However, higher levels were detected for RANTES in AD patients compared to control subjects and in AD patients treated with Donepezil. MCP-1 and RANTES have a compensatory role in balancing the impaired mechanisms involved in immune response during ageing. Our present findings suggest that these two chemokines are both involved in AD pathogenesis and might reflect different states of activation and/or responsiveness of PBMC from AD patients, contributing to the impaired of the peripheral immune system in these patients.

Muscular dystrophy with laminin deficiency decreases acetylcholinesterase activity in thymus of dystrophic Lama2dy mice

We have studied the effect of muscular dystrophy by merosin deficiency on mouse thymus acetyl- (AChE) and butyrylcholinesterase (BuChE). The organ contains AChE and BuChE activities. Merosin deficiency causes an important decrease (46%) in AChE specific activity. Thymus produces dimers, monomers and tetramers of AChE, and the three kinds of AChE mRNAs. The drop in AChE activity in dystrophic animals could affect the amount of ACh reaching cholinergic receptors in cells of lymphoid organs.

MicroRNA modulation of megakaryoblast fate involves cholinergic signaling

MicroRNAs (miRNAs) are abundant small regulatory RNAs with multiple roles in cell fate determination. The processes regulating cellular miRNA levels are still unclear and experimental oligonucleotide tools to readily mimic their effects are not yet available. Here, we report that thapsigargin-induced intracellular Ca(++) release suppressed pre-miR-181a levels in human promegakaryotic Meg-01 cells, induced differentiation-associated nuclear endoreduplication and caspase-3 activation and replaced the acetylcholinesterase 3' splice variant AChE-S with AChE-R. AChE, PKC and PKA inhibitors all attenuated the pre-miR-181a decline and the induced differentiation. AChmiON, a synthetic 23-mer 2'-oxymethylated oligonucleotide mimicking the miR-181a sequence, blocked the calcium-induced differentiation while elevating cellular pre-miR-181a levels and inducing DNA fragmentation and cell death. Moreover, when added to RW 264.7 macrophages, AChmiON at 100 nM induced nitric oxide production with efficiency close to that of bacterial endotoxin, demonstrating physiologically relevant activities also in blood-born monocytes/macrophages. The stress-induced modulation of hematopoietic miR-181a levels through AChE, PKC and PKA cascade(s) suggests using miRNA mimics for diverting the fate of hematopoietic tumor cells towards differentiation and/or apoptosis.

Expression of acetylcholine (ACh) and ACh-synthesizing activity in Archaea

Acetylcholine (ACh) is known generally as the neurotransmitter in the mammalian central and peripheral cholinergic nervous systems. However, ACh is also widely expressed in non-neuronal animal tissues and in plants, fungi and bacteria, where it is likely involved in the transport of water, electrolytes and nutrients, and in modulating various other cell functions. We have investigated the expression of ACh and ACh-synthesizing activity in various strains of Archaea, which are situated between Bacteria and Eucarya in the universal phylogenetic tree. Using a sensitive and specific radioimmunoassay, differing levels of ACh were detected in the Hyperthermophiles Thermococcus kodakaraensis KOD1, Sulfolobus tokodaii strain 7 and Pyrobaculum calidifontis VA1; the Methanogens Methanothermobacter thermautotrophicus deltaH and Methanosarcina barkeri; and the Halophiles Halobacterium sp. NRC-1 and Haloferax volcanii. T. kodakaraensis KOD1 expressed the highest levels of ACh among the Archaea tested; moreover, the substance expressed was verified to be ACh using high-performance liquid chromatography with electrochemical detection. Varying degrees of ACh-synthesizing activity were also identified in all of the strains, and the activity of bromoACh-sensitive choline acetyltransferase, an enzyme responsible for ACh synthesis in the nervous system, was detected in T. kodakaraensis KOD1. Our findings demonstrate that ACh and ACh-synthesizing activity are both expressed in evolutionally old Archaea. In the context of the recent discovery of non-neuronal ACh in bacteria, fungi, plants and animals, these findings support the notion that ACh has been expressed in organisms from the origin of life on the earth, functioning as a local mediator as well as a neurotransmitter.

Muscular dystrophy by merosin deficiency decreases acetylcholinesterase activity in thymus of Lama2dy mice

Half of congenital muscular dystrophy cases arise from laminin alpha2 (merosin) deficiency, and merosin-deficient mice (Lama2dy) exhibit a dystrophic phenotype. The abnormal development of thymus in Lama2dy mice, the occurrence of acetylcholinesterase (AChE) in the gland and the impaired distribution of AChE molecules in skeletal muscle of the mouse mutant prompted us to compare the levels of AChE mRNAs and enzyme species in thymus of control and Lama2dy mice. AChE activity in normal thymus (mean +/- SD 1.42 +/- 0.28 micromol acetylthiocholine/h/mg protein, U/mg) was decreased by approximately 50% in dystrophic thymus (0.77 +/- 0.23 U/mg) (p = 0.007), whereas butyrylcholinesterase activity was little affected. RT-PCR assays revealed variable levels of R, H and T AChE mRNAs in thymus, bone marrow and spinal cord. Control thymus contained amphiphilic AChE dimers (G2A, 64%) and monomers (G1A, 19%), as well as hydrophilic tetramers (G4H, 9%) and monomers (G1H, 8%). The dimers consisted of glycosylphosphatidylinositol-anchored H subunits. Western blot assays with anti-AChE antibodies suggested the occurrence of inactive AChE in mouse thymus. Despite the decrease in AChE activity in Lama2dy thymus, no differences between thymuses from control and dystrophic mice were observed in the distribution of AChE forms, phosphatidylinositol-specific phospholipase C sensitivity, binding to lectins and size of AChE subunits.

Regulation of CD8+ cytolytic T lymphocyte differentiation by a cholinergic pathway

In this report, we provide evidence that muscarinic receptors play a role in the generation of CD8+ cytolytic T lymphocytes. Analysis of mice with targeted deletions of each of the known muscarinic receptors (M1-M5) showed that CD8+ T cells from M1 receptor-deficient mice had a defect in the ability to differentiate into cytolytic T lymphocytes. Additional pharmacological experiments support the role of muscarinic receptors in wild type mice and suggest that acetylcholine may be involved. Together, these findings suggest that the M1 muscarinic receptor is involved in CTL development, thus providing novel insights into CD8+ T cell biology and the potential role of cholinergic signaling in immune regulation.

Lymphocyte muscarinic receptors and platelet monoamine oxidase-B as biomarkers of CNS function: effects of age and gender in healthy humans

Lymphocyte cholinergic muscarinic receptors (MRs) and platelet monoamine oxidase-B (MAO-B) activity are considered surrogate markers of the same parameters in the central nervous system. Lymphocyte MR binding and platelet MAO-B activity were measured in a consistent number of healthy human adults and analysed according to gender and age. The mean value±S.D. of MR binding neither differed between males (12.2±10.0fmol/10(6)cells, range: 0.5-37.9, n=86) and females (10.7±9.7fmol/10(6)cells, range: 0.5-39.7, n=69) nor among age groups. MAO-B activity was significantly higher in women (geometric mean: 11.3nmol/mgprotein/h, with 65% of values from 7.3 to 17.6; n=43), than in men (7.7nmol/mgprotein/h, with 65% of values from 4.5 to 13; n=95). Males aged 56-66 years displayed a higher, though not statistically significant, basal enzyme activity than younger subjects. Altogether these data indicate gender-related differences in MAO activity, but not in MR binding, and inter-individual differences in the basal values of both peripheral blood markers in healthy subjects.

Acetylcholinesterase in Hirschsprung's disease

The association between the congenital absence of colonic ganglion cells and an increased acetylcholinesterase (AChE) expression in the affected tissue is of diagnostic importance in Hirschsprung's disease (HSCR). Investigation of AChE's function in development may also help unravel some of the complex pathophysiology in HSCR. Normal nerves do not stain for AChE, but increased AChE expression is associated with the hypertrophied extrinsic nerve fibres of the aganglionic segment in HSCR. Although a high degree of histochemical diagnostic accuracy exists, results are not always uniform, and false positives and false negatives are reported. False negative results are primarily related to age, and an absence of AChE reaction does not exclude HSCR in neonates within the first 3 weeks after birth. AChE staining results may lack uniformity, resulting in a number of technical modifications that have been made to improve standardization of AChE staining. At least two distinct histological patterns are described, types A and B. The interpretation of increased AChE staining patterns in ganglionated bowel at the time of surgical pull-through remains a problem in patients with HSCR. The development of rapid staining techniques has helped to identify normal ganglionated bowel with greater certainty. The presence of fine AChE neurofibrils in the ganglionated segment has contributed to the debate surrounding intestinal neuronal dysplasia. Quantitative assay of cholinesterase activity confirms the pattern of histochemical staining. AChE is particularly increased in relation to butrylcholinesterase, with one molecular form, the G4 tetrameric form, predominating. It is likely that the raised levels of AChE in aganglionic tissue are the transcriptional consequence of the abnormalities in signalling molecules that characterize HSCR. Evidence suggests that this AChE is functioning in a nonenzymatic capacity to promote cell adhesion and differentiation and that the hypertrophied nerves and neurofibrils may be the result of this increased AChE expression.

Relationship between α7 nAChR and apoptosis in human lymphocytes

The presence of nicotinic receptors (nAChRs) in blood cells has been demonstrated. However, little is known about their functional roles. We have detected mRNA of alpha7 nAChR in peripheral human lymphocytes and determined that its expression is highly variable among individuals and within the same individual at different times. Upregulation of alpha7 is systematically observed after incubation of lymphocytes with nicotine or alpha-bungarotoxin. In addition, the incubation with these drugs decreases the percentage of apoptotic cells induced by the exposure to cortisol. Our results suggest that alpha7 nAChRs are involved in the modulation of cortisol-induced apoptosis.

Acetylcholine and choline effects on erythrocyte nitrite and nitrate levels

Acetylcholine has been detected in human blood. Acetylcholine receptors and acetylcholinesterase are present in erythrocyte membranes. We tested the acetylcholine and choline effects on nitric oxide metabolites (NOx), namely nitrites and nitrates, and observed if they are dependent on interactions with muscarinic receptors and acetylcholinesterase. Human erythrocyte suspensions were incubated with acetylcholine and choline in the absence or presence of 10 microM atropine or 10 microM velnacrine maleate. The nitrite and nitrate concentrations were determined by the Griess method. Acetylcholine or choline increased NOx control concentrations (P <0.001). The nitrite concentrations decreased in the presence of atropine or velnacrine maleate (P <0.03). The nitrate concentrations only decreased when velnacrine maleate was incubated with acetylcholine or choline (10 microM, P <0.03). These results demonstrated that acetylcholine and choline modulate nitric oxide metabolites on erythrocytes and this effect is mediated by interactions with erythrocyte membrane muscarinic receptors and membrane enzyme acetylcholinesterase. A hypothesis for the signal transduction mechanism has been discussed for acetylcholinesterase and muscarinic receptor (M1) participation.

A T-cell-dependent humoral immune response is preserved during the administration of the nerve agent pre-treatment pyridostigmine bromide in a murine model

Immune regulation, either via the autonomic nervous system or by a proposed "non-neuronal" cholinergic system, suggests that the immune system may be susceptible to perturbation by compounds affecting cholinergic function. Here, the current UK and US nerve agent pre-treatment, pyridostigmine bromide (PB) and the related anti-acetylcholinesterase (AChE) compounds physostigmine (PHY) and BW284c51 were tested for their ability to affect mouse splenocyte function in vitro. In addition, PB, at a dose equivalent to that received during pre-treatment for nerve agent poisoning, was tested for its effect on a T-cell-dependent humoral response to antigen in vivo in the mouse. None of the anti-AChEs tested affected concanavalin A (Con A)-, anti-CD3- or lipopolysaccharide LPS-driven splenocyte proliferation, in vitro, at concentrations expected to give effective nerve agent pre-treatment. However, higher concentrations (>100 microM) particularly of PHY caused some inhibition of the proliferative responses. In vivo, PB or saline was administered via 28-day mini-osmotic pumps to give a 25-40% inhibition of whole blood AChE in the PB-treated animals. During PB or saline administration, primary and secondary doses (i.p.) of sheep red blood cells (SRBC) were given and the humoral response determined by monitoring anti-SRBC IgM and IgG levels. Splenocytes isolated from the experimental animals were also examined for their proliferative and cytokine responses to stimulation. No remarkable effects of PB were seen during the period of AChE inhibition on the humoral immune response. However, a modest elevation in IL-2 and IFN(gamma) in Con A-stimulated lymphocytes was seen in PB-treated animals following pump removal. Overall these data suggest that, in vivo, the SRBC stimulated T-cell-dependent immune response is unaffected by the administration of PB at pre-treatment doses.

Role of IL-6 and IL-1beta in reactivation by acetylcholine of latently infecting pseudorabies virus

We previously reported that the latently infecting Pseudorabies virus (PrV) could be reactivated by injection of swine or mice with acetylcholine. However, the mechanism of the reactivation was not clear yet. In this study, we analyzed the kinetics of cytokines related to stress to clarify the relationship between virus reactivation by acetylcholine and the immune system. IL-6 and IL-1beta were detected in mice after stimulation with acetylcholine. This shows that acetylcholine induced physiological stress conditions. However, there seemed to be no relationship between the kinetics of the cytokine levels and PrV excretion. Moreover, neither IL-6 nor IL-1beta alone could reactivate latently infecting PrV. Thus, acetylcholine causes the reactivation of latent PrV via a mechanism not involving these immunological factors.

Autonomic neural regulation of immunity

The 'cytokine theory of disease' states that an overproduction of cytokines can cause the clinical manifestations of disease. Much effort has been expended to determine how cytokines are regulated in normal health. Transcriptional, translational and other molecular control mechanisms protect the host from excessive cytokine production. A recent discovery revealed an unexpected pathway that inhibits macrophage cytokine production. The inflammatory reflex is a physiological pathway in which the autonomic nervous system detects the presence of inflammatory stimuli and modulates cytokine production. Afferent signals to the brain are transmitted via the vagus nerve, which activates a reflex response that culminates in efferent vagus nerve signalling. Termed the 'cholinergic anti-inflammatory pathway', efferent activity in the vagus nerve releases acetylcholine (ACh) in the vicinity of macrophages within the reticuloendothelial system. ACh can interact specifically with macrophage alpha7 subunits of nicotinic ACh receptors, leading to cellular deactivation and inhibition of cytokine release. This 'hard-wired' connection between the nervous and immune systems can be harnessed therapeutically in animal models of inflammatory disease, via direct electrical stimulation of the vagus nerve, or through the use of cholinergic agonists that specifically activate the macrophage alpha7 subunit of the ACh receptor. Autonomic dysfunction has been associated with human inflammatory diseases including rheumatoid arthritis, diabetes and sepsis; whether this dysfunction results from the inflammatory component of these diseases, or is actually an underlying cause, is now less clear. The description of the cholinergic anti-inflammatory now brings to the fore several new therapeutic strategies for inflammatory disease, and suggests that many of these diseases may actually be diseases of autonomic dysfunction.

Characterization of the human nicotinic acetylcholine receptor subunit alpha (alpha) 9 (CHRNA9) and alpha (alpha) 10 (CHRNA10) in lymphocytes

Though the nicotinic acetylcholine receptor (nAChR) subunits alpha9 and alpha 10 have been thoroughly characterized within hair cells of the organ of Corti in the inner ear, prior studies have shown that they are also expressed in lymphocytes. In this report, we sought to more definitively characterize the nAChR subunits alpha9 and alpha10 within various populations of human lymphocytes. Using a combination of techniques, including RT-PCR, single-cell RT-PCR, Northern and western blot analysis, and immunofluorescence, expression of both alpha9 and alpha 10 was demonstrated in purified populations of T-cells (CD3+, CD4+, CD8+ and the Jurkat, MT2 and CEM T-cell lines) and B-cells (CD19+, CD80+ and EBV-immortalized B-cells). Single-lymphocyte recording techniques failed to identify an ionic current in response to applied acetylcholine in either T-cells or B-cells. These results clearly demonstrate the presence of these nicotinic receptor subunits within several populations of human lymphocytes, implicating their role in the immune response. However, a lack of demonstrated response to applied acetylcholine using standard single-cell recording techniques suggests a physiology different than that seen in hair cells of the inner ear.

Distribution of α7 and α4 nicotinic acetylcholine receptor subunits in several tissues of Triturus carnifex (Amphibia, Urodela)

The distribution of neuronal and non-neuronal mRNAs for alpha7 and alpha4 nicotinic acetylcholine receptor subunits was investigated in Triturus carnifex tissues using the in situ hybridization approach. The findings reveal a composite pattern of expression only partially overlapping for the two subunits; subunit alpha7 seems to be expressed widely throughout nervous, gastrointestinal and skin tissues, while alpha4 is present in a restricted number of cells of nervous and gastrointestinal tissue. We also found a specific pattern for each subunit; alpha7 and alpha4 associated exclusively to the epidermal glands and hypophysis, respectively; this is probably due to alternative roles that nicotinic acetylcholine receptors play in regulating physiological functions of non-neuronal amphibian tissues, rather than as mere neurotransmitters in the nervous system.

An in vitro investigation of the effects of the nerve agent pretreatment pyridostigmine bromide on human peripheral blood T-cell function

The current pretreatment against nerve agent poisoning deployed by the UK and US armed forces is the acetylcholinesterase (EC 3.1.1.7) inhibitor pyridostigmine bromide (PB). At higher doses, PB is also used to treat the autoimmune disease myasthenia gravis. In both cases, the therapeutic effect is mediated by inhibition of acetylcholinesterase (AChE) at cholinergic synapses. However, the location of AChE is not restricted to these sites. AChE, acetylcholine (ACh) receptors and choline acetyltransferase have been reported to be expressed by T cells, suggesting that cholinergic signalling may exert some modulatory influence on T-cell function and consequently on the immune system. The aim of this study was to investigate the role of the T-cell cholinergic system in the immunological activation process and to examine whether inhibitors of AChE such as PB affect immune function. To investigate this, human peripheral blood mononuclear cells (PBMC) were stimulated using either mitogen, cross-linking of the T-cell receptor and co-receptors with antibodies (anti-CD3/CD28) or by antigen presentation in the presence of various AChE inhibitors and ACh receptor agonists or antagonist. Several indices were used to assess T-cell activation, including the secretion of IL-2, cell proliferation and expression of CD69. Treatment with PB had no significant effect on the immunological assays selected. Physostigmine (PHY), a carbamate compound similar to PB, consistently showed inhibition of T-cell activation, but only at concentrations in excess of those required to inhibit AChE. No evidence was found to support previously published findings showing muscarinic enhancement of cell proliferation or IL-2 secretion.

Amperometric measurements of nitric oxide in erythrocytes

In the recent years, there has been an increase in the development of new biosensors that could be helpful in the study of various physiological processes. In this study, we report the development of a new in vitro experimental design for real-time nitric oxide (NO) amperometric measurements in erythrocyte suspensions. To achieve this, we employed human erythrocyte suspensions in sodium chloride 0.9%, pH 7 (haematocrit 0.05%). The production of NO by erythrocytes was measured with a commercial NO sensor during stimulation by L-arginine, acetylcholine, choline, atropine and velnacrine maleate (10 microM of final concentrations). We also measured the nitrite and nitrate concentrations produced by erythrocyte suspensions stimulated with the above effectors by means of the Griess reaction method. We observed that there was a direct relation between the electric current produced by the NO sensor, and the NO standard concentrations, thereby leading to a good calibration curve. The in vitro erythrocytes produced significant amperometric NO values in response to a wide range of effectors and these results have the same variation profile of the nitrites and nitrates results achieved with the Griess method. In conclusion, the amperometric NO sensor constitutes a reliable method for direct, and real-time measurement in vitro of the NO production of erythrocyte suspensions, As such, it offers a potential diagnostic technique for the evaluation of diseases, and the therapeutic progression of diseases, related to intracellular NO metabolism.

Blood‐cell‐specific acetylcholinesterase splice variations under changing stimuli

Developmental and trauma-induced mechanism(s) that modify inflammation and immune responses in blood cells were recently found to be regulated by acetylcholine. Here, we report corresponding blood cell-specific changes in acetylcholinesterase splice variants. Plasmon resonance and flow cytometry using acetylcholinesterase variant-specific antibody probes, revealed a progressive increase in myeloid cell fractions expressing the apoptosis-related acetylcholinesterase-S variant from newborns to adult controls and post-delivery mothers. Hematopoietic cell fractions positive for the myeloproliferative acetylcholinesterase-R variant, were similarly high in post-partum blood, both intracellular and on the cell surface. Moreover, intracellular acetylcholinesterase-S protein amounts as reflected by fluorescence intensity measurements remained unchanged in myeloid cells from post-partum mothers as compared with matched controls. Unlike brain neurons, which over-express intracellular acetylcholinesterase-R under stress, lymphocytes from post-partum mothers presented increased surface acetylcholinesterase-S and pronounced decreases in both the expression and contents of surface acetylcholinesterase-R. Peripheral stimuli-induced modulations in acetylcholine regulation may hence reflect blood cell lineage-dependent acetylcholinesterase splice variations.

From brain to blood: alternative splicing evidence for the cholinergic basis of Mammalian stress responses

Three principal features of mammalian stress responses are that they span peripheral and CNS changes, modify blood cell composition and activities, and cover inter-related alterations in a large number of gene products. The finely tuned spatiotemporal regulation of these multiple events suggests the hierarchic involvement of modulatory neurotransmitters and modified process(es) in the pathway of gene expression that together would enable widely diverse stress responses. We report evidence supporting the notion that acetylcholine (ACh) acts as a stress-response-regulating transmitter and that altered ACh levels are variously associated with changes in the alternative splicing of pre-mRNA transcripts in brain neurons and peripheral blood cells. We used acetylcholinesterase (AChE) gene expression as a case study and developed distinct probes for its alternative splice variants at the mRNA and protein levels. In laboratory animals and human-derived cells, we found stress-induced changes in the alternative splicing patterns of AChE pre-mRNA, which attributes to this gene and its different protein products diverse stress responsive functions that are associated with the enzymatic and noncatalytic properties of AChE. Together, these approaches provide a conceptually unified view of the studied pathways for controlling stress responses in brain and blood.

Expression of the cholinergic gene locus in the rat placenta

High amounts of acetylcholine (ACh) and its synthesising enzyme choline acetyltransferase (ChAT) have been detected in the placenta. Since the placenta is not innervated by extrinsic or intrinsic cholinergic neurons, placental ACh and ChAT originate from non-neuronal sources. In neurons, cytoplasmic ACh is imported into synaptic vesicles by the vesicular acetylcholine transporter (VAChT), and released through vesicular exocytosis. In view of the coordinate expression of VAChT and ChAT from the "cholinergic gene locus" in neurons, we asked whether VAChT is coexpressed with ChAT in rat placenta, and investigated this issue by means of RT-PCR, in situ hybridisation, western blot and immunohistochemistry. Messenger RNA and protein of the common type of ChAT (cChAT), its splice variant peripheral ChAT (pChAT), and VAChT were detected in rat placenta with RT-PCR and western blot. ChAT in situ hybridisation signal and immunoreactivity for cChAT and pChAT were observed in nearly all placental cell types, while VAChT mRNA and immunolabelling were detected in the trophoblast, mesenchymal cells and the visceral yolk sac epithelial cells. While ChAT is nearly ubiquitously expressed in rat placenta, VAChT immunoreactivity is localised cell type specifically, implying that both vesicular and non-vesicular ACh release machineries prevail in placental cell types.

Combinatorial Complexity of 5′ Alternative Acetylcholinesterase Transcripts and Protein Products

To explore the scope and significance of alternate promoter usage and its putative inter-relationship to alternative splicing, we searched expression sequence tags for the 5' region of acetylcholinesterase (ACHE) genes. Three and five novel first exons were identified in human and mouse ACHE genes, respectively. Reverse transcription-PCR and in situ hybridization validated most of the predicted transcripts, and sequence analyses of the corresponding genomic DNA regions suggest evolutionarily conserved promoters for each of the novel exons identified. Distinct tissue specificity and stress-related expression patterns of these exons predict combinatorial complexity with known 3' alternative AChE mRNA transcripts. Unexpectedly one of the 5' exons encodes an extended N terminus in-frame with the known AChE sequence, extending the increased complexity to the protein level. The resultant membrane variant(s), designated N-AChE, is developmentally regulated in human brain neurons and blood mononuclear cells. Alternative promoter usage combined with alternative splicing may thus lead to stress-dependent combinatorial complexity of AChE mRNA transcripts and their protein products.

Alzheimer patients treated with an AchE inhibitor show higher IL-4 and lower IL-1 beta levels and expression in peripheral blood mononuclear cells

The study evaluates the expression and production of cytokines in peripheral blood mononuclear cells of patients with Alzheimer disease treated or not treated with acetylcholinesterase inhibitor, which enhances neuronal transmission. Cytokines associated with brain inflammation such as interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha have been implicated in the regulation of amyloid peptide protein synthesis. The anti-inflammatory cytokine, IL-4, may suppress the activity of IL-1beta. Patients were assessed for clinical and immunologic features at baseline and after 1 month of treatment with Donepezil, an acetylcholinesterase inhibitor. Peripheral blood mononuclear cells were cultured with and without phytohemagglutinin stimulation. IL-1beta and IL-4 levels were measured by enzyme-linked immunosorbent assay. Reverse transcriptase-polymerase chain reaction was used to determine the expression of cytokines in peripheral mononuclear cells. Compared with untreated patients and healthy control subjects, IL-1beta levels and expression decreased in Alzheimer disease patients treated with Donepezil (P < 0.001). In contrast, IL-4 levels and expression were significantly higher in Alzheimer patients treated with the acetylcholinesterase inhibitor. This increment was observed in both unstimulated and phytohemagglutinin-stimulated peripheral blood mononuclear cells.

Synergistic control of keratinocyte adhesion through muscarinic and nicotinic acetylcholine receptor subtypes

The biological mechanisms involved in initiating, coordinating, and ultimately terminating cell-cell adhesion in the stratified epithelium are not well understood at present. This study was designed to elucidate the roles of the muscarinic M3, the nicotinic alpha3, and the mixed muscarinic-nicotinic alpha9 acetylcholine receptors in physiologic control of keratinocyte adhesion. Both muscarinic and nicotinic antagonists caused keratinocyte detachment and reversibly increased the permeability of keratinocyte monolayers, indicative of the involvement of both muscarinic and nicotinic pathways in the cholinergic control of keratinocyte adhesion. Since phosphorylation of adhesion proteins plays an important role in rapid assembly and disassembly of intercellular junctions, we measured muscarinic and nicotinic effects on phosphorylation of keratinocyte adhesion molecules. The phosphorylation levels of E-cadherin, beta-catenin, and gamma-catenin increased following pharmacological blockage of muscarinic receptors. Long-term blocking of alpha3, alpha9, and M3 receptor signaling pathways with antisense oligonucleotides resulted in cell-cell detachment and changes in the expression levels of E-cadherin, beta-catenin, and gamma-catenin in cultured human keratinocytes. Simultaneous inhibition of several receptor subtypes with a mixture of antisense oligonucleotides produced intensified abnormalities with cell adhesion. Moreover, altered cell-cell adhesion was found in the stratified epithelium of alpha3, alpha9, and M3 receptor knockout mice. Keratinocytes from these mice exhibited abnormal expression of adhesion molecules at both the protein and the mRNA levels. Thus, our data indicate that the alpha3, alpha9, and M3 acetylcholine receptors play key roles in regulating in a synergistic mode keratinocyte adhesion, most probably by modulating cadherin and catenin levels and activities. These findings may aid in the development of novel methods useful for the treatment of skin adhesion diseases and tumor metastasis.

Autonomic innervation of immune organs and neuroimmune modulation

1. Increasing evidence indicates the occurrence of functional interconnections between immune and nervous systems, although data available on the mechanisms of this bi-directional cross-talking are frequently incomplete and not always focussed on their relevance for neuroimmune modulation. 2. Primary (bone marrow and thymus) and secondary (spleen and lymph nodes) lymphoid organs are supplied with an autonomic (mainly sympathetic) efferent innervation and with an afferent sensory innervation. Anatomical studies have revealed origin, pattern of distribution and targets of nerve fibre populations supplying lymphoid organs. 3. Classic (catecholamines and acetylcholine) and peptide transmitters of neural and non-neural origin are released in the lymphoid microenvironment and contribute to neuroimmune modulation. Neuropeptide Y, substance P, calcitonin gene-related peptide, and vasoactive intestinal peptide represent the neuropeptides most involved in neuroimmune modulation. 4. Immune cells and immune organs express specific receptors for (neuro)transmitters. These receptors have been shown to respond in vivo and/or in vitro to the neural substances and their manipulation can alter immune responses. Changes in immune function can also influence the distribution of nerves and the expression of neural receptors in lymphoid organs. 5. Data on different populations of nerve fibres supplying immune organs and their role in providing a link between nervous and immune systems are reviewed. Anatomical connections between nervous and immune systems represent the structural support of the complex network of immune responses. A detailed knowledge of interactions between nervous and immune systems may represent an important basis for the development of strategies for treating pathologies in which altered neuroimmune cross-talking may be involved.

Mouse strain-specific nicotinic acetylcholine receptor expression by inhibitory interneurons and astrocytes in the dorsal hippocampus

The response by individuals to nicotine is likely to reflect the interaction of this compound with target nAChRs. However, resolving how different genetic backgrounds contribute to unique mouse strain-specific responses to this compound remains an important and unresolved issue. To examine this question in detail, expression of the nicotine acetylcholine receptor (nAChR) subunits alpha3, alpha4, alpha5, alpha7, beta2, and beta4 was measured in the dorsal hippocampus using immunohistochemistry in mouse strains or lines BALB/c, C3H/J, C57BL/6, CBA/J, DBA/2, Long Sleep (LS), Short Sleep (SS), and CF1. The nAChRs in all mice colocalized with glutamic acid decarboxylase (GAD)-positive interneurons that were subclassified into at least four groups based on nAChR subunit heterogeneity. A notable difference between mouse strains was the expression of nAChRs by astrocyte subpopulations in CA1 subregions whose numbers vary inversely with nAChR-immunostained neurons. This novel relationship also correlated with published parameters of strain sensitivity to nicotine. Attempts to identify the origin of this significant difference in nAChR expression among strains included comparison of the entire nAChRalpha4 gene sequence. Although multiple polymorphisms were identified, including two that changed nAChRalpha4 amino acid coding, none of these clearly correlate with strain-related differences in cell type-specific nAChR expression. These findings suggest that mouse strain-specific behavioral and physiological responses to nicotine are likely to be a reflection of a complex interplay between genetic factors that shape differences in expression and cellular architecture of this modulatory neurotransmitter system in the mammalian nervous system.

The endogenous, immunologically active peptide apelin inhibits lymphocytic cholinergic activity during immunological responses

We investigated the effects of apelin, an immunologically active peptide ligand for orphan receptor APJ, on acetylcholine (ACh) synthesis in MOLT-3 human leukemic T cells. We initially confirmed expression of APJ mRNA in several human T- and B-cell lines by reverse transcription-polymerase chain reaction (RT-PCR). We also found that in phytohemagglutinin (PHA)-stimulated MOLT-3 cells, an active apelin fragment, apelin-13, down-regulates expression of choline acetyltransferase (ChAT) mRNA and significantly reduces ChAT activity and cellular ACh content and release. It thus appears that apelin inhibits lymphocytic cholinergic activity via APJ during immunological responses.

[An independent, non-neuronal cholinergic system in lymphocytes and its roles in regulation of immune function]

Acetylcholine (ACh) is classically thought of as a neurotransmitter in mammalian species. However, lymphocytes express most of the cholinergic components found in the nervous system, including ACh, choline acetyltransferase (ChAT), high-affinity choline transporter, and acetylcholinesterase as well as both muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively). Activation of T cells via the T cell receptor/CD3 complex, contact of T cells with antigen presenting cells, or activation of the adenylyl cyclase pathway in T cells modulates cholinergic activity, as evidenced by up-regulation of ChAT and M(5) mAChR mRNA expression. Stimulation of mAChRs on T and B cells with ACh or another mAChR agonists elicits intracellular Ca(2+) signaling, up-regulation of c-fos expression, increased nitric oxide synthesis and interleukin-2-induced signal transduction via M(3) and M(5) mAChR-mediated pathways. Acute stimulation of nAChRs with ACh or nicotine causes rapid and transient Ca(2+) signaling in T and B cells, probably via alpha7 nAChRs subunit-mediated pathways. Chronic nicotine stimulation, by contrast, down-regulates nAChR expression and suppresses T cell activity. Abnormalities in lymphocytic cholinergic system have been seen in animal models of immune deficiency and immune acceleration. Collectively, these data provided a compelling picture in which immune function is, at least partly, under the control of an independent, non-neuronal cholinergic system in lymphocytes.

Up-regulation of lymphocytic cholinergic activity by ONO-4819, a selective prostaglandin EP4 receptor agonist, in MOLT-3 human leukemic T cells

We used a selective EP4 receptor agonist, ONO-4819, and a human leukemic T cell line MOLT-3 cells, which express all four prostaglandin E2 (PGE2) receptors (EP1-EP4), to investigate whether the EP4 PGE2 receptor subtype is involved in regulating lymphocytic cholinergic activity. Phytohemagglutinin (PHA), a T cell activator, significantly enhanced the expression of EP4 receptor mRNA during the first 3-6 h of exposure, after which, expression gradually declined. Furthermore, PHA stimulation slightly but significantly up-regulated the expression of EP2 mRNA after 12 h and of EP3 mRNA after 6 h. By contrast, expression level of EP1 receptor mRNA was not affected by PHA. ONO-4819 (1 microM), which was added to cultures after 3 h of PHA stimulation, significantly increased cellular ACh content and release, and up-regulated ChAT mRNA expression and activity but inhibited MOLT-3 cell proliferation. These findings suggest that the activation of T lymphocytes up-regulates EP4 receptor mRNA expression and, to a lesser extent, EP2 and EP3 receptors and that PGE2 enhances nonneuronal lymphocytic cholinergic transmission in activated T cells, at least in part, via EP4 receptor-mediated pathways.

Age-dependent changes in the nervous and endocrine control of the thymus

The immune system, especially the thymus, undergoes age-related modifications leading to structural and functional changes in the lymphoid organs and immunocompetent cells. Nevertheless, the consequences of thymic involution in the peripheral pool of T-cells are still a matter of controversy. The control of the thymic function is very complex and involves intrathymic signals, the autonomic nervous system, and the endocrine system. Both thymocytes and thymic stromal cells express receptors for a wide range of hormones, as well as for neurotransmitters and neuropeptides, thus affecting thymocytes maturation. This review summarizes the age-dependent variations in the extrathymic components of the thymic microenvironment, i.e., vegetative nerves and hormones, and the possible effects of those changes in the immune function.

A paradigm for single nucleotide polymorphism analysis: The case of the acetylcholinesterase gene

Acetylcholinesterase (AChE) plays a crucial physiological role in termination of impulse transmission at cholinergic synapses through rapid hydrolysis of acetylcholine. It is a highly conserved molecule, and only a few naturally occurring genetic polymorphisms have been reported in the human gene. The goal of the present study was to make a systematic effort to identify natural single nucleotide polymorphisms (SNPs) in the human ACHE gene. To this end, the genomic coding sequences for acetylcholinesterase of 96 unrelated control individuals from three distinct ethnic groups were analyzed. A total of 13 ACHE SNPs were identified, 10 of which are newly described, and five that should produce amino acid substitutions [c.101G>A (p.Arg34Gln), c.169G>A (p.Gly57Arg), c.1031A>G (p.Glu344Gly), c.1057C>A (p.His353Asn), and c.1775C>G (p.Pro592Arg)]. Population frequencies of 11 of the 13 SNPs were established in four different populations: African Americans, Ashkenazi Jews, Sephardic Jews, and Israeli Arabs; 15 haplotypes and five ethnospecific alleles were identified. The low number of SNPs identified until now in the ACHE gene is ascribed to technical hurdles arising from the high GC content and the presence of numerous repeat sequences, and does not reflect its intrinsic heterozygosity. Among the SNPs resulting in an amino acid substitution, three are within the mature protein, mapping on its external surface: they are thus unlikely to affect its catalytic properties, yet could have antigenic consequences or affect putative protein-protein interactions. Furthermore, the newly identified SNPs open the door to a study of the possible association of AChE with deleterious phenotypes-such as adverse drug responses to AChE inhibitors employed in treatment of Alzheimer patients and hypersensitivity to pesticides.

The lymphocytic cholinergic system and its contribution to the regulation of immune activity

Lymphocytes express most of the cholinergic components found in the nervous system, including acetylcholine (ACh), choline acetyltransferase (ChAT), high affinity choline transporter, muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively), and acetylcholinesterase. Stimulation of T and B cells with ACh or another mAChR agonist elicits intracellular Ca2+ signaling, up-regulation of c-fos expression, increased nitric oxide synthesis and IL-2-induced signal transduction, probably via M3 and M5 mAChR-mediated pathways. Acute stimulation of nAChRs with ACh or nicotine causes rapid and transient Ca2+ signaling in T and B cells, probably via alpha7 nAChR subunit-mediated pathways. Chronic nicotine stimulation, by contrast, down-regulates nAChR expression and suppresses T cell activity. Activation of T cells with phytohemagglutinin or antibodies against cell surface molecules enhances lymphocytic cholinergic transmission by activating expression of ChAT and M5 mAChR, which is suggestive of local cholinergic regulation of immune system activity. This idea is supported by the facts that lymphocytic cholinergic activity reflects well the changes in immune system function seen in animal models of immune deficiency and immune acceleration. Collectively, these data provide a compelling picture in which lymphocytes constitute a cholinergic system that is independent of cholinergic nerves, and which is involved in the regulation of immune function.

Nicotinic acetylcholine receptors of muscles and nerves: comparison of their structures, functional roles, and vulnerability to pathology

There are fetal and adult subtypes of muscle nicotinic receptors (AChRs), whose structures and functional roles are reasonably well known. Mutations of their subunits cause congenital myasthenic syndromes. An autoimmune response to them causes myasthenia gravis (MG). The main immunogenic region (MIR) on muscle AChRs accounts for many aspects of the pathological mechanisms by which the autoimmune response impairs neuromuscular transmission. There are many other AChR subtypes, each defined by a different combination of subunits, some of which are transiently expressed in muscle during development, others of which are expressed in keratinocytes, vascular and bronchial epithelia, and other nonneuronal cells, as well as in a wide variety of neurons. Their varied structures and functional roles are much less well known. Mutations in subunits of some of these AChRs have thus far been associated with rare forms of epilepsy and dysautonomia, but other genetic diseases associated with them probably remain to be discovered. Autoimmune responses to some of these subunits are associated with rare dysautonomias and a skin disease. The pathological mechanisms by which these autoimmune responses impair function are much less well known than in the case of MG. AChRs may provide useful drug targets in several neurological diseases. By far, the biggest direct medical impact of AChRs is addiction to tobacco, which is mediated by nicotine acting on a variety of neuronal AChRs.

Breast cancer metastasis alters acetylcholinesterase activity and the composition of enzyme forms in axillary lymph nodes

Because of the probable involvement of cholinesterases (ChEs) in tumorigenesis, this research was addressed to ascertaining whether breast cancer metastasis alters the content of acetylcholinesterase (AChE) and/or butyrylcholinesterase (BuChE) in axillary lymph nodes (LN). ChE activity was assayed in nine normal (NLN) and seven metastasis-bearing nodes (MLN) from women. AChE and BuChE forms were characterised by sedimentation analyses, hydrophobic chromatography and western blotting. The origin of ChEs in LN was studied by lectin interaction. AChE activity dropped from 21.6 mU/mg (nmol of the substrate hydrolysed per minute and per milligram protein) in NLN to 3.8 mU/mg in MLN (p < 0.001), while BuChE activity (3.6 mU/mg) was little affected. NLN contained globular amphiphilic AChE dimers (G2A, 35%), monomers (G1A, 30%), hydrophilic tetramers (G4H, 8%), and asymmetric species (A4, 23%, and A8, 4%); MLN displayed only G2A (65%) and G1A (35%) AChE forms. NLN and MLN contained G4H (79%), G4A (7%), and G1H (14%) BuChE components. Neither the binding of ChE forms with lectins and antibodies nor the subunit size were altered by metastasis. The higher level of AChE in NLN than in brain and the specific pattern of AChE forms in NLN support its role in immunity. The different profile of AChE forms in NLN and MLN may be useful for diagnosis.

Butyrylcholinesterase Activity and Pregnancy-Associated Differences in Immunologically Relevant Peripheral Blood Leukocyte Populations

PROBLEM

Toxic anticholinesterases (AC) are known contributors to negative pregnancy outcome. Impairment of detoxification mechanisms may correlate with occurrence of pregnancy disorders in Kuwait.

METHOD OF STUDY

Butyrylcholinesterase (BuChE), an enzyme which detoxifies AC was evaluated in 18 Kuwaiti women with pregnancy-induced hypertension (PIH), compared with 15 healthy pregnant and eight healthy non-pregnant women. T-lymphocyte subpopulations were measured by flow cytometry, and BuChE activity was measured by spectrophotometry.

RESULTS

Unlike the PIH group, the normal pregnancy group exhibited a significant increase in BuChE activity compared with non-pregnant control subjects (P = 0.04). Within the PIH cohort, inverse correlations were observed between BuChE activity and percentage of CD4+ CD25+ cells (P = 0.001), and CD8+ CD25+ cells (P = 0.007).

CONCLUSIONS

Elevated BuChE activity in normal pregnancy may correlate with better ability to clear pregnancy-threatening toxins, while lesser ability to do this in PIH women may be a contributor to disease. The fact that PIH subjects with large subpopulations of activated T cells also exhibited low BuChE activity further suggests a correlation between susceptibility to pregnancy loss and decreased activity of the enzyme.

The C-terminal tail of the M3-muscarinic receptor possesses anti-apoptotic properties

This study investigates the mechanisms by which the muscarinic receptor gene family can protect against apoptosis. Chinese hamster ovary cells transfected with human muscarinic receptor subtypes underwent apoptotic cell death following treatment with the DNA-damaging agent etoposide. Apoptosis was significantly reduced following muscarinic receptor stimulation of cells that were transfected with receptor subtypes that couple to the Gq/11/phospholipase C pathway, namely M1, M3, and M5. No protection was detected in cells transfected with the Gi-coupled M2 and M4 receptors. Further analysis of the Gq/11-coupled M3 receptor revealed that truncation of the carboxyl-tail (Delta 565-M3 mutant) removed the ability of the receptor to protect against etoposide-induced cell death. This mutation did not affect the ability of the receptor to signal through the phospholipase C pathway. Furthermore, activation of the Delta 565-M3 receptor resulted in robust activation of the extracellular-regulated kinase (ERK) and c-Jun kinase (JNK). The Delta 565-M3 receptor mutant also underwent agonist-driven phosphorylation in a similar manner to the wild-type receptor indicating that the anti-apoptotic effect of the M3 receptor is independent of receptor phosphorylation. Consistent with this was the fact that two M3-muscarinic receptor mutants deficient in agonist-induced receptor phosphorylation were capable of producing a full anti-apoptotic response. We conclude that the anti-apoptotic response of the muscarinic receptor family was confined to the Gq/11-coupled members of this family. The direct involvement of Gq/11/phospholipase C signaling and the ERK-1/2 and JNK pathways together with receptor phosphorylation in the anti-apoptotic response were eliminated. Mutation of a poly-basic region within the short C-terminal tail of the M3-muscarinic receptor inhibited the ability of the receptor to induce an anti-apoptotic response. We conclude that the conserved poly-basic region in the C-terminal tail of the M1, M3, and M5 receptors contributes to the ability of these receptors to mediate protection against apoptotic cell death.