Radioligand binding assay of M1-M5 muscarinic cholinergic receptor subtypes in human peripheral blood lymphocytes

PKCε stimulation of TRPV1 orchestrates carotid body responses to asthmakines

Key points

We have previously shown that carotid body stimulation by lysophosphatidic acid elicits a reflex stimulation of vagal efferent activity sufficient to cause bronchoconstriction in asthmatic rats.

Here, we show that pathophysiological concentrations of asthma‐associated prototypical Th2 cytokines also stimulate the carotid bodies.

Stimulation of the carotid bodies by these asthmakines involves a PKCε–transient receptor potential vanilloid 1 (TRPV1) signalling mechanism likely dependent on TRPV1 S502 and T704 phosphorylation sites.

As the carotid bodies’ oxygen sensitivity is independent of PKCε–TRPV1 signalling, systemic blockade of PKCε may provide a novel therapeutic target to reduce allergen‐induced asthmatic bronchoconstriction.

Consistent with the therapeutic potential of blocking the PKCε–TRPV1 pathway, systemic delivery of a PKCε‐blocking peptide suppresses asthmatic respiratory distress in response to allergen and reduces airway hyperresponsiveness to bradykinin.

Abstract

The autonomic nervous system orchestrates organ‐specific, systemic and behavioural responses to inflammation. Recently, we demonstrated a vital role for lysophosphatidic acid in stimulating the primary autonomic oxygen chemoreceptors, the carotid bodies, in parasympathetic‐mediated asthmatic airway hyperresponsiveness. However, the cacophony of stimulatory factors and cellular mechanisms of carotid body activation are unknown. Therefore, we set out to determine the intracellular signalling involved in carotid body‐mediated sensing of asthmatic blood‐borne inflammatory mediators. We employed a range of in vitro and rat in situ preparations, site‐directed mutagenesis, patch‐clamp, nerve recordings and pharmacological inhibition to assess cellular signalling. We show that the carotid bodies are also sensitive to asthma‐associated prototypical Th2 cytokines which elicit sensory nerve excitation. This provides additional asthmatic ligands contributing to the previously established reflex arc resulting in efferent vagal activity and asthmatic bronchoconstriction. This novel sensing role for the carotid body is mediated by a PKCε‐dependent stimulation of transient receptor potential vanilloid 1 (TRPV1), likely via TRPV1 phosphorylation at sites T704 and S502. Importantly, carotid body oxygen sensing was unaffected by blocking either PKCε or TRPV1. Further, we demonstrate that systemic PKCε blockade reduces asthmatic respiratory distress in response to allergen and airway hyperresponsiveness. These discoveries support an inflammation‐dependent, oxygen‐independent function for the carotid body and suggest that targeting PKCε provides a novel therapeutic option to abate allergic airway disease without altering life‐saving autonomic hypoxic reflexes.

We have previously shown that carotid body stimulation by lysophosphatidic acid elicits a reflex stimulation of vagal efferent activity sufficient to cause bronchoconstriction in asthmatic rats.

Here, we show that pathophysiological concentrations of asthma‐associated prototypical Th2 cytokines also stimulate the carotid bodies.

Stimulation of the carotid bodies by these asthmakines involves a PKCε–transient receptor potential vanilloid 1 (TRPV1) signalling mechanism likely dependent on TRPV1 S502 and T704 phosphorylation sites.

As the carotid bodies’ oxygen sensitivity is independent of PKCε–TRPV1 signalling, systemic blockade of PKCε may provide a novel therapeutic target to reduce allergen‐induced asthmatic bronchoconstriction.

Consistent with the therapeutic potential of blocking the PKCε–TRPV1 pathway, systemic delivery of a PKCε‐blocking peptide suppresses asthmatic respiratory distress in response to allergen and reduces airway hyperresponsiveness to bradykinin.

Increased expression of blood muscarinic receptors in patients with reflex syncope

AIMS

Pathophysiology of reflex syncope is not fully understood but a vagal overactivity might be involved in this syncope. Previously, overexpression of muscarinic M2 receptors and acetylcholinesterase was found in particular in the heart and in lymphocytes of rabbits with vagal overactivity as well as in hearts of Sudden Infant Death Syndromes. The aim of this present study was to look at M2 receptor expression in blood of patients with reflex syncope. The second objective was to measure acetylcholinesterase expression in these patients.

METHODS AND RESULTS

136 subjects were enrolled. This monocenter study pooled 45 adults exhibiting recurrent reflex syncope compared with 32 healthy adult volunteers (18-50 years) and 38 children exhibiting reflex syncope requiring hospitalization compared with 21 controls (1-17 years). One blood sample was taken from each subject and blood mRNA expression of M2 receptors was assessed by qRT-PCR. Taking into account the non-symmetric distributions of values in both groups, statistical interferences were assessed using bayesian techniques. A M2 receptor overexpression was observed in adult and pediatric patients compared to controls. The medians [q1;q3] were 0.9 [0.3;1.9] in patients versus 0.2 [0.1;1.0] in controls; the probability that M2 receptor expression was higher in patients than in controls (Pr[patients>controls]) was estimated at 0.99. Acetylcholinesterase expression was also increased 0.7 [0.4;1.6] in patients versus 0.4 [0.2;1.1] in controls; the probability that acetylcholinesterase expression was higher in patients than in controls (Pr[patients>controls]) was estimated at 0.97. Both in adults and children, the expression ratio of M2 receptors over acetylcholinesterase was greater in the patient group compared with the control group.

CONCLUSION

M2 receptor overexpression has been detected in the blood of both, adults and children, exhibiting reflex syncope. As in our experimental model, i.e. rabbits with vagal overactivity, acetylcholinesterase overexpression was associated with M2 receptor overexpression. For the first time, biological abnormalities are identified in vagal syncope in which only clinical signs are, so far, taken into account for differential diagnosis and therapeutic management. Further work will be needed to validate potential biomarkers of risk or severity associated with the cholinergic system.

Modified expression of peripheral blood lymphocyte muscarinic cholinergic receptors in asthmatic children

Lymphocytes possess an independent cholinergic system. We assessed the expression of muscarinic cholinergic receptors in lymphocytes from 49 asthmatic children and 10 age matched controls using Western blot. We demonstrated that CD4+ and CD8+ T cells expressed M2 and M4 muscarinic receptors which density were significantly increased in asthmatic children in comparison with controls. M2 and M4 receptor increase was strictly related with IgE and fraction of exhaled nitric oxide (FeNO) measurements and with impairment in objective measurements of airway obstruction. Increased lymphocyte muscarinic cholinergic receptor expression may concur with lung cholinergic dysfunction and with inflammatory molecular framework in asthma.

Muscarinic receptor agonists and antagonists: effects on inflammation and immunity

In this chapter, we will review what is known about muscarinic regulation of immune cells and the contribution of immune cell muscarinic receptors to inflammatory disease and immunity. In particular, immune cell expression of cholinergic machinery, muscarinic receptor subtypes and functional consequences of agonist stimulation will be reviewed. Lastly, this chapter will discuss the potential therapeutic effects of selective antagonists on immune cell function and inflammatory disease in recent animal studies and human clinical trials.

Effects of paraoxon on neuronal and lymphocytic cholinergic systems

The cholinergic system in lymphocytes is hypothesized to be a key target for neurotoxic organophosphates (OPs). The present study determined the comparative effects of paraoxon, the active metabolite of OP-parathion, which is detected in the human neuroblastoma line, SH-SY5Y, and leukemic T-lymphocytes, MOLT-3, in vitro. Paraoxon induced cytotoxic effects in a dose- and time-dependent manner in both cells. Further, the paraoxon-induced modulatory effects were comparable despite different cell types, including over-expression of N-terminus acetylcholinesterase (N-AChE) protein, a marker of apoptosis, down-regulations of mRNA encoding M1, M2, and M3 muscarinic acetylcholine receptors (mAChRs), and induction in expression of c-Fos gene, an indication of certain mAChR subtype(s) activation. Furthermore, the non-selective cholinergic antagonist atropine partially attenuated the paraoxon-induced N-AChE and c-Fos activations in both types of cells. These results provide initial and additional information that OPs may similarly induce neuro- and immuno-toxic effects through mAChRs activation, and they underline the potential of using lymphocytes for assessing OPs-induced neurotoxicity.

In vitro and in vivo interactions of aluminum on NTPDase and AChE activities in lymphocytes of rats

Al adjuvants are used in vaccines to increase the immune response. NTPDase and AChE play a pivotal role and act in the regulation of the immune system. The effect of Al exposure in vitro and in vivo on NTPDase and AChE activities in the lymphocytes of rats was determined. In vitro, ATP hydrolysis was decreased by 20.4% and 17.3% and ADP hydrolysis was decreased by 36.5% and 34.8%, in groups D and E, respectively, when compared to the control. AChE activity was increased by 157.3%, 152.5%, 74.7% and 90.8% in groups B, C, D, and E, respectively, when compared to the control. In vivo, ATP hydrolysis was increased by 85% and 86% and ADP hydrolysis was increased by 104.2% and 74%, in Al plus citrate and Al groups, respectively, when compared to the control. AChE activity was increased by 50.7% in Al plus citrate and by 28.6% in Al groups, when compared to the control. Our results show that Al exposure both in vitro and in vivo altered NTPDase and AChE activities in lymphocytes. These results may demonstrate the ability of Al to elicit the immune system, where NTPDase and AChE activities can act as purinergic and cholinergic markers in lymphocytes.

Regulation of M2, M3, and M4 muscarinic receptor expression in K562 chronic myelogenous leukemic cells by carbachol

CONTEXT

Muscarinic receptors mediate a variety of cellular responses to acetylcholine, including inhibition of adenylate cyclase, breakdown of phosphoinositide and modulation of ion channels. These receptors are relatively abundant in the central nervous system and peripheral parasympathetic nervous system. Many cells express a mixture of muscarinic receptor transcripts. Changes in muscarinic M(2) and M(3) receptor mRNA levels in response to agonist treatment have been reported in cerebellar granule cells, Chinese hamster ovary cells, lymphocytes and in the human neuroblastoma cell line SH-SY5Y.

OBJECTIVE

In this study, we investigated the effects of agonist stimulation on cell proliferation and on the levels of muscarinic receptor expression in K562 chronic myelogenous leukemia cells.

METHODS

Total RNA and crude membrane fractions were prepared from K562 cells challenged with carbachol (CCh). Muscarinic receptor subtype expression was determined by RT-PCR and western blot analysis. Proliferation and cell viability were evaluated by the trypan blue exclusion test and BrDU labeling.

RESULTS

We showed that CCh-treatment leads to changes in muscarinic M(2), M(3), and M(4) receptor transcripts as well as M(2) and M(3) protein levels. We also found that CCh decreased proliferation of K562 cells in a time dependent manner, an effect prevented by atropine. These results suggest that CCh modulates K562 chronic myelogenous leukemic cells proliferation through muscarinic acetylcholine receptors.

Reduced platelet monoamine oxidase type B activity and lymphocyte muscarinic receptor binding in unmedicated children with attention deficit hyperactivity disorder

Several lines of evidence support the role of monoaminergic and cholinergic dysregulation in attention deficit hyperactivity disorder (ADHD) and the concept that peripheral blood neurotransmission indices may represent valuable surrogate CNS markers. We determined platelet MAO-B activity (p-MAO-B) and lymphocyte muscarinic cholinergic receptor binding (l-MR) in 44 unmedicated ADHD children (aged 9.1 +/- 2.87 years) and in 26 age-matched controls for comparison. Lower levels of p-MAO-B (approximately 35%) and l-MR (approximately 55%) in ADHD were observed compared with controls. Differences were gender-dependent: p-MAO-B was reduced in males only (5.20 +/- 2.99 vs 8.46 +/- 5.1 nmol mg(-1) protein h(-1) in ADHD and controls, respectively) and l-MR in females only (ADHD vs control: 6.63 +/- 1.75 and 15.30 +/- 8.35 fmol 10(-6) cells). The clinical significance was corroborated by the correlation between these markers and severity of specific symptoms: lower p-MAO-B associated with increased inattention scores (Conners' teacher-rating scale); lower l-MR associated with increased score for oppositional-defiant disorder (ODD) (SNAP-IV); and trend towards correlation between increased inattention (SNAP-IV) and lower l-MR.

No changes in lymphocyte muscarinic receptors and platelet monoamine oxidase-B examined as surrogate central nervous system biomarkers in a Faroese children cohort prenatally exposed to methylmercury and polychlorinated biphenyls

Experimental evidence suggests that monoamine oxidase B (MAO-B) and muscarinic cholinergic receptors (mAChRs) are involved in the pathogenesis of neurotoxicity caused by methylmercury and polychlorinated biphenyls (PCBs). Blood samples from 7-year-old exposed children were analyzed for platelet MAO-B and lymphocyte mAChRs as potential markers of exposure to these neurotoxicants. The blood neurotoxicity biomarkers were compared with prenatal and current exposures and with neuropsychological test results. Both biomarkers showed homogeneous distributions within this cohort (mAChR, range 0.04-36.78 fmol/million cells; MAO-B, 0.95-14.95 nmol mg(-1) protein h(-1)). No correlation was found between the two biomarkers and either blood neurotoxicant concentrations or clinical findings. MAO-B and mAChR sensitivity may not be sufficiently high to assess early, subclinical responses to low/moderate methylmercury and/or PCB exposure, whereas these markers are significantly altered in sustained exposure scenarios, as shown by clinical studies in drug addicts or patients treated with psychopharmacological agents.

Targeting the cholinergic system as a therapeutic strategy for the treatment of pain

Acetylcholine mediates its effects through both the nicotinic acetylcholine receptors (ligand-gated ion channels) and the G protein-coupled muscarinic receptors. It plays pivotal roles in a diverse array of physiological processes and its activity is controlled through enzymatic degradation by acetylcholinesterase. The effects of receptor agonists and enzyme inhibitors, collectively termed cholinomimetics, in antinociception/analgesia are well established. These compounds successfully inhibit pain signaling in both humans and animals and are efficacious in a number of different preclinical and clinical pain models, suggesting a broad therapeutic potential. In this review we examine and discuss the evidence for the therapeutic exploitation of the cholinergic system as an approach to treat pain.

Changes in muscarinic cholinergic receptor expression in human peripheral blood lymphocytes in allergic rhinitis patients

BACKGROUND

Parasympathetic nerves provide the dominant autonomic innervation of the upper and lower airways. They release acetylcholine that, activating post-junctional muscarinic receptors, causes bronchoconstriction, mucous secretion and vasodilation. Dysfunction of the upper and lower airways frequently coexist, and they appear to share key elements of pathogenesis.

OBJECTIVE

The present study has assessed the expression and pattern of cholinergic muscarinic receptor subtypes in peripheral blood lymphocytes harvested from allergic rhinitis patients with different degree of bronchial hyperresponsiveness detected by methacholine challenge test.

METHODS

Radioligand binding assay for determining the density of muscarinic cholinergic receptor subtypes; immunoblot analysis for assessing the characteristic of muscarinic cholinergic receptor subtype protein and immunocytochemical techniques for investigating the cellular localization of receptors.

RESULTS

An increased expression of M2 and M5 receptor proteins was observed in peripheral blood lymphocytes of allergic rhinitis patients in comparison with healthy control individuals. M3 receptor subtype decreased in allergic rhinitis patients with normal or mild responses to methacholine. A trend versus a return to normal value was found in moderate and severe responders. No changes of the M4 receptor subtype were found.

CONCLUSIONS AND CLINICAL IMPLICATIONS

Increase in M2 receptor expression correlated with disease severity and bronchial hyperreactivity. Changes in muscarinic cholinergic receptor expression in allergic rhinitis underline a role of cholinergic system of immune cells in allergic airway disease.

CAPSULE SUMMARY

Studies addressed to rhinitis and asthma have identified many similarities. Our results indicate that changes in peripheral blood lymphocyte muscarinic receptor expression may reflect the cholinergic involvement into allergic airway diseases.

Microarray profiling of lymphocytes in internal diseases with an altered immune response: potential and methodology

Recently it has become possible to investigate expression of all human genes with microarray technique. The authors provide arguments to consider peripheral white blood cells and in particular lymphocytes as a model for the investigation of pathophysiology of asthma, RA, and SLE diseases in which inflammation is a major component. Lymphocytes are an alternative to tissue biopsies that are most often difficult to collect systematically. Lymphocytes express more than 75% of the human genome, and, being an important part of the immune system, they play a central role in the pathogenesis of asthma, RA, and SLE. Here we review alterations of gene expression in lymphocytes and methodological aspects of the microarray technique in these diseases. Lymphocytic genes may become activated because of a general nonspecific versus disease-specific mechanism. The authors suppose that in these diseases microarray profiles of gene expression in lymphocytes can be disease specific, rather than inflammation specific. Some potentials and pitfalls of the array technologies are discussed. Optimal clinical designs aimed to identify disease-specific genes are proposed. Lymphocytes can be explored for research, diagnostic, and possible treatment purposes in these diseases, but their precise value should be clarified in future investigation.

Noradrenergic and cholinergic neural pathways mediate stress-induced reactivation of colitis in the rat

Evidence to date suggests that stress-induced exacerbation or relapse of intestinal inflammation in inflammatory bowel disease requires both activation of the autonomic nervous system and the activation of the immune system by the presence of previously encountered luminal antigens. The aim of the present study was to further explore these associations and to determine the role of the autonomic nervous in modulating the intestinal inflammatory response to stress. Rats healed from an initial dinitrobenzene sulfonic acid-induced colitis were given a non-colitic dose of dinitrobenzene sulfonic acid (dissolved in saline) or 0.9% saline intra-rectally and then subjected to restraint stress. Cardiac sympathovagal balance was assessed by power spectral analysis of heart rate variability data collected from telemetric electrocardiogram recordings before, during and post stress. Only rats that were stressed and received dinitrobenzene sulfonic acid showed an inflammatory relapse characterized by significant macroscopic damage and elevated myeloperoxidase activity associated with a significant infiltration of mucosal and submucosal T lymphocytes. No difference in inflammatory markers was observed in animals that received intra-rectal saline and restraint stress. Rats subjected to stress and intra-rectal dinitrobenzene sulfonic acid demonstrated an increase in sympathetic activity with a nearly four fold increase in LF:HF ratio during stress and a significant increase in heart rate. Shortly after cessation of stress, the LF:HF ratio decreased significantly, returning to baseline levels, however the heart rate remained significantly elevated over baseline levels following stress, but decreased to a level that was significantly lower than during stress. The stress/dinitrobenzene sulfonic acid-induced relapses were preventable by pre-treating rats with hexamethonium (a nicotinic cholinergic ganglion blocking agent) or the co-administration of atropine (a muscarinic cholinoceptor antagonist) and bretylium (a noradrenergic ganglion blocking agent), but was not prevented when either atropine or bretylium were administered alone. This study utilizes an established model of chemically induced colitis that when integrated with stress results in relapsing inflammatory bowel disease. Moreover, this study demonstrates that noradrenergic and cholinergic neural pathways mediate the stress response critical for the relapse of colitis.

Muscarinic cholinergic receptor subtypes in cerebral cortex of Fisher 344 rats: a light microscope autoradiography study of age-related changes

The density and localization of muscarinic cholinergic M1-M5 receptor subtypes was investigated in frontal and occipital cortex of male Fisher 344 rats aged 6 months (young-adult), 15 months (mature) and 22 months (senescent) by combined kinetic and equilibrium binding and light microscope autoradiography. In 6-month-old rats, the rank order density of muscarinic cholinergic receptor subtypes was M1>M2>M4>M3>M5 both in frontal and occipital cortex. A not homogeneous distribution of different receptor subtypes throughout cerebrocortical layers of frontal or occipital cortex was found. In frontal cortex silver grains corresponding to the M1 and M2 receptor subtypes were decreased in 15- and 22-month-old groups. The M3 receptor density was remarkably and moderately decreased in layers II/III and V, respectively, of rats aged 15 and 22 months. A reduced M4 receptor density was observed in layer I and to a lesser extent in layer V of mature and senescent rats, whereas no age-related changes of M5 receptor were found. In occipital cortex a diminution of M1 receptor was observed in layers II/III and V of mature and senescent rats. The M2 receptor expression decreased in layer I of 15- and 22-month-old senescent rats, whereas M3-M5 receptors were unchanged with exception of a slight decrease of the M4 receptor in layer IV and of M5 receptor in layers II/III. These findings indicate a different sensitivity to aging of muscarinic receptor subtypes located in various cerebrocortical layers. This may account for the difficulty in obtaining relevant results in manipulating cholinoceptors to counter age-related impairment of cholinergic system.

Lymphocyte cytochrome c oxidase, cyclic GMP and cholinergic muscarinic receptors as peripheral indicators of carbon monoxide neurotoxicity after acute and repeated exposure in the rat

Changes in cerebral cytochrome oxidase (COX) activity, nitric oxide (NO)-cyclic GMP (cGMP) pathway and cholinergic muscarinic receptors (MRs) have been reported in rodents acutely exposed to carbon monoxide (CO). These endpoints measurable in lymphocytes may serve as peripheral markers of CO neurotoxicity. The early and delayed effects of repeated and acute in vivo CO inhalation were investigated on COX activity, cGMP formation and MR binding in rat brain and lymphocytes to assess whether each endpoint was similarly affected both centrally and peripherally. Male Wistar rats either inhaled 500 ppm CO, 6 h/day, 5 days/week, 4 weeks (repeated exposure) or 2,400 ppm, 1 h (single exposure). Neither treatment altered brain or lymphocyte COX activity 1 and 7 days post-treatment. Also ineffective were repeated and acute CO treatments towards (3)H-quinuclidinyl benzilate (QNB) binding to MRs in cerebral cortex, hippocampus, striatum, cerebellum (respective controls, mean+/-S.D.: 171 +/- 45, 245 +/- 53, 263 +/- 14 and 77 +/- 7 fmol/mg protein) and lymphocytes (24 +/- 10 fmol/million cells) at the same time points. In lymphocytes control cGMP levels averaged 1.98 +/- 0.99 pmol/mg protein under basal conditions, and 3.94 +/- 0.55 pmol/mg protein after NO-stimulation. One day after chronic treatment cessation, the CO-treated group displayed about a 50% decrease in both basal and NO-stimulated cGMP values, which persisted up to 7 days after, compared to air-exposed rats. Acutely, CO caused a delayed enhancement (+140%) of NO-induced activation of soluble guanylate cyclase. The finding that the NO-cGMP pathway is a target for the delayed effects of CO in peripheral blood cells is in accordance with our data in brain [Hernández-Viadel, M., Castoldi, A.F., Coccini, T., Manzo, L., Erceg, S., Felipo, V., 2004. In vivo exposure to carbon monoxide causes delayed impairment of activation of soluble guanylate cyclase by nitric oxide in rat brain cortex and cerebellum. Journal of Neurochemistry 89, 1,157-1,165], and supports the use of this peripheral endpoint as a biomarker of CO central effects.

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.

Functional analysis of muscarinic acetylcholine receptors using knockout mice

Because of the low selectivity of available ligands, pharmacological approaches to elucidate the functional difference among muscarinic acetylcholine receptor (mAChR) subtypes have been problematic. As an alternative approach, we have established a series of mutant mouse lines deficient in each mAChR subtype (mAChR KO mice). The systematic analyses of these mice have been useful in revealing the functional difference among mAChR subtypes. Here, we review our prior research on these mutant mice and also some notable findings reported by other research groups.

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.

Potential clozapine target sites on peripheral hematopoietic cells and stromal cells of the bone marrow

The antipsychotic drug clozapine, acts via interaction with selective neurotransmitter receptor systems. Its use however, is associated with life-threatening agranulocytosis. The mechanism by which this occurs and its possible relationship with the drug's atypicality remain unclear. As a first step in identifying mechanistic pathways involved, profiling of neurotransmitter receptors on human neutrophils, mononuclear and bone marrow stromal cells as putative targets for clozapine-mediated toxicity was undertaken. Expression of mRNA encoding dopaminergic d2, d3, d4; serotonergic 5ht2a, 5ht2c, 5ht3, 5ht6, 5ht7; adrenergic alpha1a, alpha2; histaminergic h1 and muscarinic m1, m2, m3, m4, m5 receptors was analyzed by reverse transcription-polymerase chain reaction methods. While 5ht2c, 5ht6, m1 and m2 mRNA were undetected, the presence of the other receptors indicates sites at which clozapine could bind and induce toxicity of neutrophils and stromal components which regulate granulopoiesis. The functional significance of differential receptor expression while unknown, may argue for neural regulation of hematopoiesis.

Cholinergic pathways modulate experimental dinitrobenzene sulfonic acid colitis in rats

Recent studies have suggested that neuroimmune interactions modulate intestinal mucosal immune responses. In the current study, we examined the role of cholinergic pathways in modulating the severity of acute dinitrobenzene sulfonic acid colitis, using pharmacological agents to suppress acetylcholinesterase in Sprague-Dawley rats, and evaluating the colitis in the cholinergic hyperresponsive Flinder's sensitive line rats and their control counterparts, the Flinder's resistant line. Colitis was induced by intrarectal dinitrobenzene sulfonic acid (80 mg x ml(-1) in 50% ethanol); controls received intrarectal saline. Sprague-Dawley rats received an acetylcholinesterase inhibitor, physostigmine (50 microg x kg(-1) s.c.) or neostigmine (50 microg x kg(-1) s.c.), 30 min prior to intrarectal dinitrobenzene sulfonic acid; controls received saline vehicle. On day 5, the macroscopic damage score, myeloperoxidase activity (an estimate of granulocyte infiltration) and smooth muscle thickness were evaluated in the inflamed colonic segment. Significant increases in macroscopic damage score and colonic smooth muscle thickness were observed in Sprague-Dawley and Flinder's Resistant Line rats on day 5 following intrarectal dinitrobenzene sulfonic acid compared to saline controls. Increased myeloperoxidase activity was also observed in dinitrobenzene sulfonic acid-treated Sprague-Dawley rats and Flinder's Resistant Line rats. In contrast, Flinder's Sensitive Line rats failed to demonstrate a significant rise in macroscopic damage, smooth muscle layer thickness, or myeloperoxidase activity on day 5 following intrarectal dinitrobenzene sulfonic acid when compared to saline-treated Flinder's Sensitive Line controls. Neostigmine and physostigmine treatment prior to intrarectal dinitrobenzene sulfonic acid significantly attenuated macroscopic damage score, myeloperoxidase activity and smooth muscle thickness on day 5 compared to colitic Sprague-Dawley controls. Significantly greater reductions in myeloperoxidase activity were observed with physostigmine vs. neostigmine pretreatment. These data suggest that cholinergic pathways modulate the acute colonic inflammatory response associated with the dinitrobenzene sulfonic acid model, with central pathways exerting a greater protective effect relative to peripheral pathways. Further studies are required to determine the contributions of sites in the nervous system and neuro-effector junctions.

Sequence variation in the promoter region of the cholinergic receptor muscarinic 3 gene and asthma and atopy

BACKGROUND

Muscarinic acetylcholine receptors are members of the superfamily of G protein-coupled, 7 transmembrane- spanning proteins. They are important in the development of airway hyperresponsiveness. In the lung the M3 receptor, encoded by the cholinergic receptor muscarinic 3 gene, is present in airway smooth muscle and mediates smooth muscle contraction.

OBJECTIVE

We considered the cholinergic receptor muscarinic 3 gene as a possible candidate gene for bronchial asthma and initiated studies to identify polymorphisms in the promoter region.

METHOD

We identified 4 single-nucleotide polymorphisms (-708A/G, -627G/C, -513C/A, and -492C/T) and 2 short tandem repeat polymorphisms, a tetranucleotide (CTTT)12-20 and a dinucleotide (GT)6-19 repeat.

RESULTS

None of the identified single nucleotide polymorphisms were significantly more frequent in asthmatic patients (n = 76) compared with in healthy control subjects (n = 81). Furthermore, there was no evidence for nonrandom transmission of short tandem repeat polymorphism haplotypes to individuals with asthma or bronchial hyperresponsiveness (P >.50) in a large Hutterite pedigree. However, there was significant nonrandom transmission of haplotypes to individuals with skin test reactivity to cockroach allergens (global transmission disequilibrium test: chi2 = 38.55, P =.013).

CONCLUSIONS

These results suggest a possible role for this gene in atopic disorders.

Immunochemical and immunocytochemical characterization of cholinergic markers in human peripheral blood lymphocytes

Cholinergic markers and the expression of M(2)-M(5) muscarinic cholinergic receptor subtypes were investigated in human peripheral blood lymphocytes by Western blot analysis and immunocytochemistry. The totality of peripheral blood lymphocytes express acetylcholine (ACh) immunoreactivity, choline acetyltransferase (ChAT), acetylcholinesterase (AChE), vesicular ACh transporter (VAChT) and M(2)-M(5) muscarinic cholinergic receptor protein immunoreactivity. Western blot analysis performed independently on T and B lymphocytes using anti-ChAT and anti-AChE antibodies revealed labelling of single bands of approximately 68-70 and 70 kDa, respectively, whereas VAChT was bound to two bands of approximately 80 and 45 kDa. The pattern of immunoblotting was similar in membranes of lymphocytes and striatum, used as a reference brain tissue. Western blot analysis using anti M(2)-M(5) receptor antibodies revealed labelling of single bands of approximately 55, 85-90, 50 and 81 kDa, respectively. Confocal laser immunofluorescence showed the localization of ACh and VAChT immunoreactivity in punctiform areas likely corresponding to cytoplasmic vesicles. ChAT and AChE were diffused to the cytoplasm and plasma membrane. Muscarinic receptor immunoreactivity was located in lymphocyte plasma membrane. Although the role of lymphocyte cholinergic system is still unclear, the demonstration of cholinergic markers in T and B human blood lymphocytes supports the view that a cholinergic systems may contribute to the regulation of immune function. The characterization of these cholinergic markers may also contribute to define if their evaluation can be used for assessing the status of brain cholinergic system.

Expression of peripheral blood lymphocyte muscarinic cholinergic receptor subtypes in airway hyperresponsiveness

The expression of muscarinic cholinergic receptor subtypes was investigated in peripheral blood lymphocytes (PBL) of bronchial asthma patients by a combined kinetic and equilibrium labeling technique for radioligand binding assay of muscarinic cholinergic receptor subtypes and by receptor immunochemistry and immunocytochemistry. An increased expression of M2 and to a lesser extent of M5 receptors and no changes of M4 receptor were observed in PBL of asthmatics compared to control individuals. The increase was related to bronchial hyperresponsiveness detected by methacholine challenge test. Analysis of M3 receptor expression revealed biphasic changes, with a decreased receptor density in patients with normal, mild and moderate responses to methacholine test and a recovery to levels similar to those found in healthy individuals in severe responders to methacholine test. The demonstration of a different expression of lymphocyte muscarinic receptors in asthma suggests that cholinergic system may participate to a molecular framework influencing immune functions in asthma.

Nimodipine prevents scopolamine-induced impairments in object recognition

The effects of acute administration of the dihydropyridine calcium channel antagonist, nimodipine, were studied on the actions of scopolamine in the object recognition test. Scopolamine at 0.125 mg/kg decreased the difference in the time spent exploring novel and familiar objects when given either 15 min before, or immediately after, exposure to objects. Administration of nimodipine at 10 mg/kg, or 1 mg/kg, at the same time as the scopolamine completely prevented the deleterious effects on memory in this task. This effect was seen when nimodipine and/or scopolamine were given prior to the object exposure and also when the drugs were given after the experience of seeing the objects. Nimodipine had no effects on performance when given in the absence of scopolamine. This lack of change in total time spent exploring the objects indicated that the effects of scopolamine and nimodipine were not due to changes in motor coordination or alertness. The results are discussed in the light of the role of cholinergic transmission in memory and the known actions of dihydropyridines on brain function.

Structure and transcription of the human m3 muscarinic receptor gene

We have isolated and characterized the human m3 muscarinic receptor gene and its promoter. Using 5' rapid amplification of cDNA ends (RACE), internal polymerase chain reaction (PCR), and homology searching to identify EST clones, we determined that the cDNA encoding the m3 receptor comprises 4,559 bp in 8 exons, which are alternatively spliced to exclude exons 2, 4, 6, and/or 7; the receptor coding sequence occurs within exon 8. Analysis of P1 artificial chromosome (PAC) and bacterial artificial chromosome (BAC) clones and of PCR- amplified genomic DNA, and homology searching of human chromosome 1 sequence provided from the Sanger Centre (Hinxton, Cambridge, UK) revealed that the m3 muscarinic receptor gene spans at least 285 kb. A promoter fragment containing bp -1240 to +101 (relative to the most 5' transcription start site) exhibited considerable transcriptional activity during transient transfection in cultured subconfluent, serum-fed canine tracheal myocytes, and 5' deletion analysis of promoter function revealed the presence of positive transcriptional regulatory elements between bp -526 and -269. Sequence analysis disclosed three potential AP-2 binding sites in this region; five more AP-2 consensus binding motifs occur between bp -269 and +101. Cotransfection with a plasmid expressing human AP-2alpha substantially increased transcription from m3 receptor promoter constructs containing 526 or 269 bp of 5' flanking DNA. Furthermore, m3 receptor promoter activity was enhanced by long-term serum deprivation of canine tracheal myocytes, a treatment that is known to increase AP-2 transcription-promoting activity in these cells. Together, these data suggest that expression of the human m3 muscarinic receptor gene is regulated in part by AP-2 in airway smooth muscle.

Peripheral blood lymphocytes muscarinic cholinergic receptor subtypes in Alzheimer's disease: a marker of cholinergic dysfunction?

Muscarinic M2-M5 muscarinic cholinergic receptors were investigated in peripheral blood lymphocytes of patients with mild cognitive impairment of the Alzheimer's type (MCIAT), probable Alzheimer's disease (AD) and probable vascular dementia (VaD). [3H]-N-methyl scopolamine (NMS) in the presence of muscarinic antagonists and Mamba venom to occlude different receptor subtypes was used as radioligand. Analysis of [3H]-NMS binding curves without receptor subtype assessment resulted in a slight decrease of receptor density in AD patients. Evaluation of receptor subtypes in MCIAT and AD patients revealed a decrease of M3 receptor by more than 50%, an increase of M4 receptor expression by about 20% and no changes of M2 or M5 receptors. The expression of M2-M5 receptors was unaltered in VaD patients. Strong positive and negative correlations respectively were found between the density of lymphocyte M3 and M4 receptors and MMSE score in both MCIAT (0.78 for M3 receptor and 0.80 for M4 receptor) and AD (0.82 for M3 receptor and 0.83 for M4 receptor) patients. These findings suggest that changes in the expression of peripheral blood lymphocyte M3 and M4 receptors in AD are related to the degree of cognitive impairment. Assessment of lymphocyte muscarinic receptor subtypes may contribute to characterization of cholinergic impairment in AD.

Cholinergic dilation of cerebral blood vessels is abolished in M(5) muscarinic acetylcholine receptor knockout mice

The M(5) muscarinic receptor is the most recent member of the muscarinic acetylcholine receptor family (M(1)-M(5)) to be cloned. At present, the physiological relevance of this receptor subtype remains unknown, primarily because of its low expression levels and the lack of M(5) receptor-selective ligands. To circumvent these difficulties, we used gene targeting technology to generate M(5) receptor-deficient mice (M5R(-/-) mice). M5R(-/-) mice did not differ from their wild-type littermates in various behavioral and pharmacologic tests. However, in vitro neurotransmitter release experiments showed that M(5) receptors play a role in facilitating muscarinic agonist-induced dopamine release in the striatum. Because M(5) receptor mRNA has been detected in several blood vessels, we also investigated whether the lack of M(5) receptors led to changes in vascular tone by using several in vivo and in vitro vascular preparations. Strikingly, acetylcholine, a powerful dilator of most vascular beds, virtually lost the ability to dilate cerebral arteries and arterioles in M5R(-/-) mice. This effect was specific for cerebral blood vessels, because acetylcholine-mediated dilation of extra-cerebral arteries remained fully intact in M5R(-/-) mice. Our findings provide direct evidence that M(5) muscarinic receptors are physiologically relevant. Because it has been suggested that impaired cholinergic dilation of cerebral blood vessels may play a role in the pathophysiology of Alzheimer's disease and focal cerebral ischemia, cerebrovascular M(5) receptors may represent an attractive therapeutic target.

Therapeutic opportunities from muscarinic receptor research

Muscarinic acetylcholine receptor subtypes have been the subjects of research for at least a quarter of a century. Nonetheless, there are few selective muscarinic receptor ligands presently used as therapeutics. The extensive development of muscarinic M(1) receptor agonists for the treatment of cognitive dysfunction has culminated in a series of unsuccessful drug candidates, which reflects a lack of understanding of the disease and the role played by muscarinic cholinergic transmission. Paradoxically, the most successful antagonist approved for use in urinary incontinence is the nonselective muscarinic receptor antagonist tolterodine. This deficit in subtype-selective ligands could be circumvented by the development of transgenic mice, each lacking functional M(1), M(2), M(3), M(4) or M(5) receptors. In this article, the current status of muscarinic receptor research is critically assessed.

Action of tacrine on muscarinic receptors in rat intestinal smooth muscle

1. The reversible cholinesterase inhibitor, tacrine (THA) was examined against the contractions of rat duodenum to acetylcholine and carbachol (cholinesterase resistant). 2. Tacrine (10(-6) M) showed a similar behaviour to physostigmine (10(-6) M), changing the characters of the concentration-response curve to Ach. The contractual responses were shifted to the left at low concentrations of ACh to reveal a bell-shaped curve with declaring contradictions at high concentrations of ACh. 3. Antagonism by atropine (10(-8) M) was reduced in the presence of tacrine (10.54, dose-ratio) compared with the shift of the curve in the absence of tacrine (73.9, dose-ratio). The declining phase of the concentration-response curve to ACh was also antagonized by atropine. 4. Further evidence for muscarininc receptor antagonism by tacrine was a small rightward shift of the concentration-response curve for carbachol, an agonist immune to cholinesterase. 5. This study has shown that tacrine acts both as a cholinesterase inhibitor and muscarinic antagonist on rat intestinal smooth muscle.

Muscarinic cholinergic receptors subtypes in rat cerebellar cortex: light microscope autoradiography of age-related changes

Muscarinic cholinergic M1-M5 receptor subtypes were investigated in the cerebellar cortex of Fischer 344 rats aged 6 (young), 15 (adult) and 22 months (senescent) by combined kinetic and equilibrium binding and light microscope autoradiography. In young rats the rank order of receptor density was M5<M4<M3 and M3<M5<M4 in the molecular and granular layers, respectively. M1, M2, M4 and M5 receptors were also observed within Purkinje neurons. M1 receptor did not show age-related changes as well as the M2 receptor in the molecular layer. In this layer, M3-M5 receptors were increased in senescent compared to younger rats. In the granular layer the expression of M2 and M5 muscarinic receptors was similar in young and senescent rats and higher in adult rats. M3 and M4 receptors were more in adult and senescent rats compared to young animals. In Purkinje neurons, a slight-to-moderate age-related increase of M1 and M5 receptor expression was observed.

Human esophageal smooth muscle cells express muscarinic receptor subtypes M(1) through M(5)

Receptor characterization in human esophageal smooth muscle is limited by tissue availability. We used human esophageal smooth muscle cells in culture to examine the expression and function of muscarinic receptors. Primary cultures were established using cells isolated by enzymatic digestion of longitudinal muscle (LM) and circular muscle (CM) obtained from patients undergoing esophagectomy for cancer. Cultured cells grew to confluence after 10-14 days in medium containing 10% fetal bovine serum and stained positively for anti-smooth muscle specific alpha-actin. mRNA encoding muscarinic receptor subtypes M(1)-M(5) was identified by RT-PCR. The expression of corresponding protein for all five subtypes was confirmed by immunoblotting and immunocytochemistry. Functional responses were assessed by measuring free intracellular Ca(2+) concentration ([Ca(2+)](i)) using fura 2 fluorescence. Basal [Ca(2+)](i), which was 135 +/- 22 nM, increased transiently to 543 +/- 29 nM in response to 10 microM ACh in CM cells (n = 8). This response was decreased <95% by 0.01 microM 4-diphenylacetoxy-N-methylpiperidine, a M(1)/M(3)-selective antagonist, whereas 0.1 microM methoctramine, a M(2)/M(4)-selective antagonist, and 0.1 microM pirenzepine, a M(1)-selective antagonist, had more modest effects. LM and CM cells showed similar results. We conclude that human smooth muscle cells in primary culture express five muscarinic receptor subtypes and respond to ACh with a rise in [Ca(2+)](i) mediated primarily by the M(3) receptor and involving release of Ca(2+) from intracellular stores. This culture model provides a useful tool for further study of esophageal physiology.