Acetylcholine as a mitogen: muscarinic receptor-mediated proliferation of rat astrocytes and human astrocytoma cells

Muscarinic acetylcholine receptors present in human osteoblast and bone tissue

Acetylcholine is the predominant neurotransmitter in the neuromuscular junction, and a role in bone has been postulated. The expression of nicotinic receptors has been reported in osteoblasts, but the expression and function of muscarinic receptor in bone remain obscure. In this study, we investigated the expression and functional activities of muscarinic receptor subtypes in human osteoblast cell lines and animal and human bone tissue. The mRNA levels of muscarinic receptor subtypes were detected by reverse-transcription polymerase chain reaction. We found that muscarinic subtypes m1, m2, m3, m4, and m5 were expressed at different levels in human osteosarcoma HOS cells, rat femur, and human rib bone tissue; m1, m4, m5 were in cultured mouse femur bone cells and cultured mouse calvarial bone cells; m2, m3, m4 were in bovine bone. The mRNA of neuronal markers, light-, medium- and heavy-neurofilament, was not found in human bone tissues to exclude the possible contamination from neuronal tissue. Methacholine induced an elevation in cytosolic calcium concentration and proliferation in HOS cells. Both effects were blocked by atropine. We conclude that muscarinic receptor is present in bone tissue to evoke calcium signaling and modulate cell proliferation. Different muscarinic receptor subtypes are distributed in various parts of the animal skeletal system including the different species and bone portions. Bone remodeling involving osteoblast proliferation leads the possibilities that muscarinic receptor may play roles in bone remodeling.

Developmental aspects of the cholinergic system

Beyond its importance in sustaining or modulating different aspects of the activity of the central nervous system (CNS), the cholinergic system plays important roles during development. In the current review, we focus on the developmental aspects associated with major components of the cholinergic system: Acetylcholine, choline acetyltransferase, vesicular acetylcholine transporter, high-affinity choline transporter, acetylcholinesterase, nicotinic and muscarinic receptors. We describe when and where each one of these components is first identified in the CNS and the changes in their levels that occur during the course of prenatal and postnatal development. We also describe how these components are relevant to many events that occur during the development of the CNS, including progenitor cells proliferation and differentiation, neurogenesis, gliogenesis, neuronal maturation and plasticity, axonal pathfinding, regulation of gene expression and cell survival. It will be noticed that evidence regarding the developmental aspects of the cholinergic system comes mostly from studies that used agonists, such as nicotine, and antagonists, such as hemicholinium-3. Studies using immunohistochemistry and genetically altered mice also provided valuable information.

Locally produced relaxin may affect testis and vas deferens function in rats

We have previously shown that the rat testis and vas deferens contain high levels of the relaxin receptor, RXFP1. The present study was undertaken to determine the expression of relaxin in these tissues, and the effect of exogenous relaxin on Sertoli cell proliferation and on the mRNA levels of some proteins that may contribute to epithelial secretion and tissue reorganization in the vas deferens. Relaxin mRNA levels in testis and vas deferens were much lower than in the prostate. Sertoli cells seem to be an important source of relaxin mRNA in testis. Relaxin immunoreactivity was detected in the seminiferous epithelium but not in the interstitial compartment. The relaxin precursor was expressed in the vas deferens, and relaxin immunoreactivity was detected in apical cells of the vas deferens. Castration, but not treatment with the anti-estrogen ICI 182,780, dramatically reduced relaxin mRNA levels in the prostate and vas deferens, and this effect was prevented by testosterone.Rxfp1mRNA levels in the vas deferens and prostate were not affected by castration or treatment with ICI 182,780. Exogenous relaxin increased the incorporation of3H-thymidine in cultured Sertoli cells, and treatment of the vas deferens with 100 ng/ml relaxin increased the mRNA levels for the cystic fibrosis chloride channel (cystic fibrosis transmembrane regulator) about three times, and doubled mRNA levels for the inducible form of nitric oxide synthase and metalloproteinase 7. These results suggest that locally produced relaxin acts as an autocrine or paracrine agent in the testis and vas deferens to affect spermatogenesis and seminal fluid composition.

Ethanol inhibits muscarinic receptor-induced axonal growth in rat hippocampal neurons

BACKGROUND

In utero alcohol exposure can lead to fetal alcohol spectrum (FAS) disorders characterized by cognitive and behavioral deficits. In vivo and in vitro studies have shown that ethanol alters neuronal development. One mechanism through which ethanol has been shown to exert its effects is the perturbation of activated signaling cascades. The cholinergic agonist carbachol has been shown to induce axonal outgrowth through intracellular calcium mobilization, protein kinase C (PKC) activation, and ERK1/2 phosphorylation. This study investigated the effect of ethanol on the differentiation of rat hippocampal pyramidal neurons induced by carbachol as a possible mechanism involved in the developmental neurotoxicity of ethanol.

METHODS

Prenatal rat hippocampal pyramidal neurons were treated with ethanol (50 to 75 mM) in the presence or absence of carbachol for 24 hours. Neurite outgrowth was assessed spectrophotometrically; axonal length was measured in neurons fixed and immunolabeled with the neuron-specific betaIII tubulin antibody; cytotoxicity was analyzed using the thiazolyl blue tetrazolium bromide assay. The effect of ethanol on carbachol-stimulated intracellular calcium mobilization was assessed utilizing the fluorescent calcium probe, Fluo-3AM. The PepTag(R) assay for nonradioactive detection of PKC from Promega was used to measure PKC activity, and ERK1/2 activation was determined by densitometric analysis of Western blots probed for phospo-ERK1/2.

RESULTS

Ethanol treatment (50 to 75 mM) caused an inhibition of carbachol-induced axonal growth, without affecting neuronal viability. Neuron treatment for 15 minutes with ethanol did not inhibit the carbachol-stimulated rise in intracellular calcium, while inhibiting PKC activity at the highest tested concentration and ERK1/2 phosphorylation at both the concentrations used in this study. On the other hand, neuron treatment for 24 hours with ethanol significantly inhibited carbachol-induced increase in intracellular calcium.

CONCLUSIONS

Ethanol inhibited carbachol-induced neurite outgrowth by inhibiting PKC and ERK1/2 activation. These effects may be, in part, responsible for some of the cognitive deficits associated with in utero alcohol exposure.

Infusion of gliotoxins or a gap junction blocker in the prelimbic cortex increases alcohol preference in Wistar rats

Postmortem research has revealed that there is a lower density of glial cells in regions of the prefrontal cortex (PFC) of uncomplicated alcoholics when compared with control subjects. Impairment of astrocyte function in the PFC may contribute to malfunction in circuits involved in emotion- and reward-related subcortical centers, heavily connected with the PFC and directly involved in the pathophysiology of addictive behaviours. The hypothesis was tested that infusion of gliotoxins known to injure astrocytes or of a gap junction blocker into the prelimbic area of the rat PFC results in increased preference for ethanol in rats exposed to free choice between water and 10% ethanol. Fluorocitric acid, L-alpha-aminoadipic acid (AAD) or the gap junction blocker 18-alpha-glycyrrhetinic acid (AGA) were bilaterally infused once into the rat prelimbic cortex and alcohol preference (ratio of 10% ethanol consumed to total liquid ingested) was measured before and after infusion. Infusion of AAD or AGA dissolved in their vehicles, but not of their vehicles alone, resulted in significant transient increase of preference for 10% ethanol. The present data suggest that impaired integrity of glial cells or the gap junctional communication between them in the rat PFC may contribute to changes in ethanol preference.

Manganese inhibits the ability of astrocytes to promote neuronal differentiation

Manganese (Mn) is a known neurotoxicant and developmental neurotoxicant. As Mn has been shown to accumulate in astrocytes, we sought to investigate whether Mn would alter astrocyte-neuronal interactions, specifically the ability of astrocytes to promote differentiation of neurons. We found that exposure of rat cortical astrocytes to Mn (50-500 microM) impaired their ability to promote axonal and neurite outgrowth in hippocampal neurons. This effect of Mn appeared to be mediated by oxidative stress, as it was reversed by antioxidants (melatonin and PBN) and by increasing glutathione levels, while it was potentiated by glutathione depletion in astrocytes. As the extracellular matrix protein fibronectin plays an important role in astrocyte-mediated neuronal neurite outgrowth, we also investigated the effect of Mn on fibronectin. Mn caused a concentration-dependent decrease of fibronectin protein and mRNA in astrocytes lysate and of fibronectin protein in astrocyte medium; these effects were also antagonized by antioxidants. Exposure of astrocytes to two oxidants, H2O2 and DMNQ, similarly impaired their neuritogenic action, and led to a decreased expression of fibronectin. Mn had no inhibitory effect on neurite outgrowth when applied directly onto hippocampal neurons, where it actually caused a small increase in neuritogenesis. These results indicate that Mn, by targeting astrocytes, affects their ability to promote neuronal differentiation by a mechanism which is likely to involve oxidative stress.

The activation of M1 muscarinic receptor signaling induces neuronal differentiation in pyramidal hippocampal neurons

Muscarinic receptors have been proposed to play an important role during brain development by regulating cell survival, proliferation, and differentiation. This study investigated the effect of muscarinic receptor activation on prenatal rat hippocampal pyramidal neuron differentiation and the signal transduction pathways involved in this effect. The cholinergic agonist carbachol, after 24 h in vitro, increased the length of the axon, without affecting the length of minor neurites. Carbachol-induced axonal growth was also observed in pyramidal neurons from the neocortex but not in granule neurons from the cerebellum. The effect of carbachol was mediated by the M(1) subtype of muscarinic receptors. The Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester, the two protein kinase C (PKC) inhibitors 3-[1-[3-(dimethylaminopropyl]-1H-indol-3-yl]-4-(1H-indol-3-yl)-1H-pyrrole-2,5-dione monohydrochloride (GF109203X) and 2-[8-[(dimethylamino)methyl]-6,7,8,9-tetrahydropyridol[1,2-a]indol-3-yl]-3-(1-methylindol-3-yl)maleimide (Ro-32-0432), and the extracellular signal-regulated kinase (ERK)1/2 inhibitors 2'-amino-3'-methoxyflavone (PD98059) and 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene (U0126) all blocked carbachol-induced axonal outgrowth. In addition, down-regulation of ERK1/2 with small interfering RNA abolished the neuritogenic effect of carbachol. These data suggest an involvement of Ca(2+), PKC, and ERK1/2 in carbachol-induced axonal growth. Carbachol indeed increased the release of Ca(2+) from intracellular stores and induced PKC and ERK1/2 activation. Additional experiments showed that PKC, but not Ca(2+), is involved in carbachol-induced ERK1/2 activation. Together, these results show that cholinergic stimulation of prenatal hippocampal pyramidal neurons accelerates axonal growth through the induction of Ca(2+) mobilization and the activation of PKC and especially of ERK1/2.

Shotgun proteomics implicates extracellular matrix proteins and protease systems in neuronal development induced by astrocyte cholinergic stimulation

Astrocytes play an important role in neuronal development through the release of soluble factors that affect neuronal maturation. Shotgun proteomics followed by gene ontology analysis was used in this study to identify proteins present in the conditioned medium of primary rat astrocytes. One hundred and thirty three secreted proteins were identified, the majority of which were never before reported to be produced by astrocytes. Extracellular proteins were classified based on their biological and molecular functions; most of the identified proteins were involved in neuronal development. Semi-quantitative proteomic analysis was carried out to identify changes in the levels of proteins released by astrocytes after stimulation with the cholinergic agonist carbachol, as we have previously reported that carbachol-treated astrocytes elicit neuritogenesis in hippocampal neurons through the release of soluble factors. Carbachol up-regulated secretion of 15 proteins and down-regulated the release of 17 proteins. Changes in the levels of four proteins involved in neuronal differentiation (thrombospondin-1, fibronectin, plasminogen activator inhibitor-1, and plasminogen activator urokinase) were verified by western blot or ELISA. In conclusion, this study identified a large number of proteins involved in neuronal development in the astrocyte secretome and implicated extracellular matrix proteins and protease systems in neuronal development induced by astrocyte cholinergic stimulation.

Muscarinic receptors and ligands in cancer

Emerging evidence indicates that muscarinic receptors and ligands play key roles in regulating cellular proliferation and cancer progression. Both neuronal and nonneuronal acetylcholine production results in neurocrine, paracrine, and autocrine promotion of cell proliferation, apoptosis, migration, and other features critical for cancer cell survival and spread. The present review comprises a focused critical analysis of evidence supporting the role of muscarinic receptors and ligands in cancer. Criteria are proposed to validate the biological importance of muscarinic receptor expression, activation, and postreceptor signaling. Likewise, criteria are proposed to validate the role of nonneuronal acetylcholine production in cancer. Dissecting cellular mechanisms necessary for muscarinic receptor activation as well as those needed for acetylcholine production and release will identify multiple novel targets for cancer therapy.

Modulation of neuritogenesis by astrocyte muscarinic receptors

Astrocytes have been shown to release factors that have promoting or inhibiting effects on neuronal development. However, mechanisms controlling the release of such factors from astrocytes are not well established. Astrocytes express muscarinic receptors whose activation stimulates a robust intracellular signaling, although the role of these receptors in glial cells is not well understood. Acetylcholine and acetylcholine receptors are present in the brain before synaptogenesis occurs and are believed to be involved in neuronal maturation. The present study was undertaken to investigate whether stimulation of muscarinic receptors in astrocytes would modulate neurite outgrowth in hippocampal neurons. Rat hippocampal neurons, co-cultured with rat cortical astrocytes previously exposed to the cholinergic agonist carbachol, displayed longer neurites. The effect of carbachol in astrocytes was due to the activation of M3 muscarinic receptors. Exposure of astrocytes to carbachol increased the expression of the extracellular matrix proteins fibronectin and laminin-1 in these cells. This effect was mediated in part by an increase in laminin-1 and fibronectin mRNA levels and in part by the up-regulation of the production and release of plasminogen activator inhibitor-1, an inhibitor of the proteolytic degradation of the extracellular matrix. The inhibition of fibronectin activity strongly reduced the effect of carbachol on the elongation of all the neurites, whereas inhibition of laminin-1 activity reduced the elongation of minor neurites only. Plasminogen activator inhibitor-1 also induced neurite elongation through a direct effect on neurons. Taken together, these results demonstrate that cholinergic muscarinic stimulation of astrocytes induces the release of permissive factors that accelerate neuronal development.

Neurotoxicity of a polybrominated diphenyl ether mixture (DE-71) in mouse neurons and astrocytes is modulated by intracellular glutathione levels

Polybrominated diphenyl ether (PBDE) flame retardants have become widespread environmental contaminants. Body burden in the U.S. population has been shown to be higher than in other countries, and infants and toddlers have highest exposure through maternal breast milk and household dust. The primary concern for adverse health effects of PBDEs relates to their potential developmental neurotoxicity, which has been found in a number of animal studies. Information on the possible mechanisms of PBDE neurotoxicity is limited, though some studies have suggested that PBDEs may elicit oxidative stress. The present study examined the in vitro neurotoxicity of DE-71, a penta-BDE mixture, in primary neurons and astrocytes obtained from wild-type and Gclm knockout mice, which lack the modifier subunit of glutamate-cysteine ligase and, as a consequence, have very low levels of glutathione (GSH). These experiments show that neurotoxicity of DE-71 in these cells is modulated by cellular GSH levels. Cerebellar granule neurons (CGNs) from Gclm (-/-) mice displayed a higher sensitivity to DE-71 toxicity compared to CGNs from wild-type animals. DE-71 neurotoxicity in CGNs from Gclm (+/+) mice was exacerbated by GSH depletion, and in CGNs from both genotypes it was antagonized by increasing GSH levels and by antioxidants. DE-71 caused an increase in reactive oxygen species and in lipid peroxidation in CGNs, that was more pronounced in Gclm (-/-) mice. Toxicity of DE-71 was mostly due to the induction of apoptotic cell death. An analysis of DE-71-induced cytotoxicity and apoptosis in neurons and astrocytes from different brain areas (cerebellum, hippocampus, cerebral cortex) in both mouse genotypes showed a significant correlation with intracellular GSH levels. As an example, DE-71 caused cytotoxicity in hippocampal neurons with IC50s of 2.2 and 0.3 microM, depending on genotype, and apoptosis with IC50s of 2.3 and 0.4 microM, respectively. These findings suggest that the developmental neurotoxicity of PBDE may involve oxidative stress, and that individual with genetic polymorphisms leading to lower GSH levels may be more susceptible to their adverse effects.

Rho-family GTPases modulate Ca(2+) -dependent ATP release from astrocytes

Previously, we reported that activation of G protein-coupled receptors (GPCR) in 1321N1 human astrocytoma cells elicits a rapid release of ATP that is partially dependent on a G(q)/phophospholipase C (PLC)/Ca(2+) mobilization signaling cascade. In this study we assessed the role of Rho-family GTPase signaling as an additional pathway for the regulation of ATP release in response to activation of protease-activated receptor-1 (PAR1), lysophosphatidic acid receptor (LPAR), and M3-muscarinic (M3R) GPCRs. Thrombin (or other PAR1 peptide agonists), LPA, and carbachol triggered quantitatively similar Ca(2+) mobilization responses, but only thrombin and LPA caused rapid accumulation of active GTP-bound Rho. The ability to elicit Rho activation correlated with the markedly higher efficacy of thrombin and LPA, relative to carbachol, as ATP secretagogues. Clostridium difficile toxin B and Clostridium botulinum C3 exoenzyme, which inhibit Rho-GTPases, attenuated the thrombin- and LPA-stimulated ATP release but did not decrease carbachol-stimulated release. Thus the ability of certain G(q)-coupled receptors to additionally stimulate Rho-GTPases acts to strongly potentiate a Ca(2+)-activated ATP release pathway. However, pharmacological inhibition of Rho kinase I/II or myosin light chain kinase did not attenuate ATP release. PAR1-induced ATP release was also reduced twofold by brefeldin treatment suggesting the possible mobilization of Golgi-derived, ATP-containing secretory vesicles. ATP release was also markedly repressed by the gap junction channel inhibitor carbenoxolone in the absence of any obvious thrombin-induced change in membrane permeability indicative of hemichannel gating.

Imidacloprid induces neurobehavioral deficits and increases expression of glial fibrillary acidic protein in the motor cortex and hippocampus in offspring rats following in utero exposure

Imidacloprid, a neonicotinoid, is one of the fastest growing insecticides in use worldwide because of its selectivity for insects. The potential for neurotoxicity following in utero exposure to imidacloprid is not known. Timed pregnant Sprague-Dawley rats (300-350 g) on d 9 of gestation were treated with a single intraperitoneal injection (i.p.) of imidacloprid (337 mg/kg, 0.75 x LD50, in corn oil). Control rats were treated with corn oil. On postnatal day (PND) 30, all male and female offspring were evaluated for (a) acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activity, (b) ligand binding for nicotinic acetylcholine receptors (nAChR) and muscarinic acetylcholine receptors (m2 mAChR), (c) sensorimotor performance (inclined plane, beam-walking, and forepaw grip), and (d) pathological alterations in the brain (using cresyl violet and glial fibrillary acidic protein [GFAP] immunostaining). The offspring of treated mothers exhibited significant sensorimotor impairments at PND 30 during behavioral assessments. These changes were associated with increased AChE activity in the midbrain, cortex and brainstem (125-145% increase) and in plasma (125% increase). Ligand binding densities for [3H]cytosine for alpha4beta2 type nAchR did not show any significant change, whereas [3H]AFDX 384, a ligand for m2mAChR, was significantly increased in the cortex of offspring (120-155% increase) of imidacloprid-treated mothers. Histopathological evaluation using cresyl violet staining did not show any alteration in surviving neurons in various brain regions. On the other hand, there was a rise in GFAP immunostaining in motor cortex layer III, CA1, CA3, and the dentate gyrus subfield of the hippocampus of offspring of imidacloprid-treated mothers. The results indicate that gestational exposure to a single large, nonlethal, dose of imidacloprid produces significant neurobehavioral deficits and an increased expression of GFAP in several brain regions of the offspring on PND 30, corresponding to a human early adolescent age. These changes may have long-term adverse health effects in the offspring.

17beta-estradiol induces the translocation of the estrogen receptors ESR1 and ESR2 to the cell membrane, MAPK3/1 phosphorylation and proliferation of cultured immature rat Sertoli cells

The aim of the present study was to determine the mechanisms involved in estrogen actions in cultured rat Sertoli cells. RT-PCR detected transcripts for the estrogen receptors ESR1 and ESR2 in cultured immature Sertoli cells and in the testis of 15-, 28-, and 120-day-old rats. The expression of ESR1 and ESR2 was confirmed in Sertoli cells by immunofluorescence and Western blot. Immunohistochemistry with cryosections of testes from immature and adult rats revealed that ESR1 is present in Sertoli, Leydig, and some peritubular myoid cells, and ESR2 is present in multiple cell types, including germ cells. Treatment of Sertoli cells with 17beta-estradiol (E(2)) induced a translocation of ESR1 and ESR2 to the plasma membrane and a concomitant phosphorylation of MAPK3/1. Both effects reached a maximum after 10 min and were blocked by PP2, an inhibitor of the SRC family of protein tyrosine kinases, and by the antiestrogen ICI 182,780 (ICI). MAPK3/1 phosphorylation was also decreased in the presence of AG 1478, an inhibitor of the epidermal growth factor receptor (EGFR) kinase, and in the presence of MAP2K1/2 inhibitor UO126. Treatment with E(2) for 24 h increased the incorporation of [methyl-(3)H]thymidine, which was blocked by ICI. These results indicate that E(2) activates an SRC-mediated translocation of estrogen receptors to the plasma membrane, which results in the activation of EGFR and the mitogen-activated protein kinase signaling pathway. In addition, activation of ESR1 and/or ESR2 by E(2) is involved in proliferation of immature Sertoli cells. The estrogen actions in Sertoli cells might be a key step mediating cellular events important for spermatogenesis and fertility.

An in vitro approach to assess the toxicity of certain food contaminants: Methylmercury and polychlorinated biphenyls

Methylmercury (MeHg) and polychlorinated biphenyls (PCBs) are widespread environmental pollutants and food contaminants, and known developmental neurotoxicants. Aim of this study was to evaluate the effects of MeHg, PCB 126 and PCB 153 in a battery of in vitro cell systems. A total of 17 cell types were utilized, including nervous system (neuronal and astroglial) and non-nervous system cells. End-points measured included MTT reduction, Trypan blue exclusion and (3)H-thymidine incorporation into DNA. Results indicate that this approach would identify these three compounds as neurotoxicants, and would also point out to the thyroid (for PCB 126 and MeHg) and the prostate (for both PCBs) as important additional targets. Tests of binary combinations of MeHg and PCBs indicated no interaction and an additive response, in agreement with other recent reports. Cerebellar granule neurons from mice with genetically determined low glutathione levels were more sensitive than wild-type neurons to the toxicity of all three compounds, supporting a role for oxidative stress in their neurotoxicity. These findings provide initial evidence that a relatively rapid in vitro screening approach can be developed, that would provide initial information useful for assessing neurotoxicity, as well as indication on potential other targets of biological action or toxicity.

M3 muscarinic receptor antagonists inhibit small cell lung carcinoma growth and mitogen-activated protein kinase phosphorylation induced by acetylcholine secretion

The importance of acetylcholine as a neurotransmitter in the nervous system is well established, but little is yet known about its recently described role as an autocrine and paracrine hormone in a wide variety of nonneuronal cells. Consistent with the expression of acetylcholine in normal lung, small cell lung carcinoma (SCLC) synthesize and secrete acetylcholine, which acts as an autocrine growth factor through both nicotinic and muscarinic cholinergic mechanisms. The purpose of this study was to determine if interruption of autocrine muscarinic cholinergic signaling has potential to inhibit SCLC growth. Muscarinic receptor (mAChR) agonists caused concentration-dependent increases in intracellular calcium and mitogen-activated protein kinase (MAPK) and Akt phosphorylation in SCLC cell lines. The inhibitory potency of mAChR subtype-selective antagonists and small interfering RNAs (siRNAs) on acetylcholine-increased intracellular calcium and MAPK and Akt phosphorylation was consistent with mediation by M3 mAChR (M3R). Consistent with autocrine acetylcholine secretion stimulating MAPK and Akt phosphorylation, M3R antagonists and M3R siRNAs alone also caused a decrease in basal levels of MAPK and Akt phosphorylation in SCLC cell lines. Treatment of SCLC cells with M3R antagonists inhibited cell growth both in vitro and in vivo and also decreased MAPK phosphorylation in tumors in nude mice in vivo. Immunohistochemical staining of SCLC and additional cancer types showed frequent coexpression of acetylcholine and M3R. These findings suggest that M3R antagonists may be useful adjuvants for treatment of SCLC and, potentially, other cancers.

Control of cell proliferation by neurotransmitters in the developing vertebrate retina

In the developing vertebrate retina, precise coordination of retinal progenitor cell proliferation and cell-cycle exit is essential for the formation of a functionally mature retina. Unregulated or disrupted cell proliferation may lead to dysplasia, retinal degeneration or retinoblastoma. Both cell-intrinsic and -extrinsic factors regulate the proliferation of progenitor cells during CNS development. There is now growing evidence that in the developing vertebrate retina, both slow and fast neurotransmitter systems modulate the proliferation of retinal progenitor cells. Classic neurotransmitters, such as GABA (gamma-amino butyric acid), glycine, glutamate, ACh (acetylcholine) and ATP (adenosine triphosphate) are released, via vesicular or non-vesicular mechanisms, into the immature retinal environment. Furthermore, these neurotransmitters signal through functional receptors even before synapses are formed. Recent evidence indicates that the activation of purinergic and muscarinic receptors may regulate the cell-cycle machinery and consequently the expansion of the retinal progenitor pool. Interestingly, GABA and glutamate appear to have opposing roles, inducing retinal progenitor cell-cycle exit. In this review, we present recent findings that begin to elucidate the roles of neurotransmitters as regulators of progenitor cell proliferation at early stages of retinal development. These studies also raise several new questions, including how these neurotransmitters regulate specific cell-cycle pathways and the mechanisms by which retinal progenitor cells integrate the signals from neurotransmitters and other exogenous factors during vertebrate retina development.

Ethanol induces cholesterol efflux and up-regulates ATP-binding cassette cholesterol transporters in fetal astrocytes

Cholesterol plays an important role during brain development, since it is involved in glial cell proliferation, neuronal survival and differentiation, and synaptogenesis. Astrocytes produce large amounts of brain cholesterol and produce and release lipoproteins containing apoE that can extract cholesterol from CNS cells for elimination. We hypothesized that some of the deleterious effects of ethanol in the developing brain may be due to the disruption of cholesterol homeostasis in astrocytes. This study investigates the effect of ethanol on cholesterol efflux mediated by ATP-binding cassette (ABC) cholesterol transporters. In fetal rat astrocytes in culture, ethanol caused a concentration-dependent increase in cholesterol efflux and increased the levels of ABCA1 starting at 25 mm. Similar effects of ethanol on cholesterol efflux and ABCA1 were also observed in fetal human astrocytes. In addition, ABCA1 levels were increased in the brains of 7-day-old pups treated for 3 days with 2, 4, or 6 g/kg ethanol. Ethanol also increased apoE release from fetal rat astrocytes, and conditioned medium prepared from ethanol-treated astrocytes extracted more cholesterol than conditioned medium from untreated cells. In addition, ethanol increased the levels of another cholesterol transporter, ABCG1. Ethanol did not affect cholesterol synthesis and reduced the levels of intracellular cholesterol in rat astrocytes. Retinoic acid, which induces teratogenic effects similarly to ethanol, also caused up-regulation of ABCA1 and ABCG1.

Reduced glial and neuronal packing density in the orbitofrontal cortex in alcohol dependence and its relationship with suicide and duration of alcohol dependence

BACKGROUND

Reduced metabolism, blood flow, and tissue volume have been detected in the dorsolateral prefrontal cortex (dlPFC) of neurologically intact alcoholic subjects and these deficits are accompanied by lower density of neurons and glial cells. Another prefrontal region, the orbitofrontal cortex (ORB), functionally and structurally differentiated from the dlPFC, and heavily involved in decision-making processes, also shows functional alterations in alcoholic subjects. However, it is unknown whether changes in the packing density of neurons or glial cells also occur in the ORB and whether that density may be related to the increased suicide probability of alcoholic subjects or to the duration of alcohol dependence.

METHODS

The present study used a 3-dimensional cell-counting method in postmortem brain tissue to determine the packing density of neurons and glial cells in the ORB (area 47) of 15 subjects with alcohol dependence (8 suicides, 7 nonsuicides) and 8 normal controls and to determine whether cell density is correlated with suicide and duration of alcohol dependence.

RESULTS

There was a significantly lower density of both neurons (by 27%) and glial cells (by 25%) in the ORB of alcoholic subjects compared with controls. Packing density of either neurons or glial cells was not significantly different in alcoholic suicides compared with alcoholic nonsuicides. Age was not correlated with neuronal or glial density in either group. However, the duration of alcohol dependence and the ratio of that duration to the length of life span were significantly and negatively correlated to the overall density of neurons.

CONCLUSION

The present results indicate that alcohol dependence is associated with a decrease in the packing density of neurons and glia in the ORB and that the reduction in neuronal but not glial density progresses with the duration of alcohol dependence.

Intravesical pressure induces hyperplasia and hypertrophy of human bladder smooth muscle cells mediated by muscarinic receptors

PURPOSE

Bladder outlet obstruction with intravesical pressures exceeding 40 cmH(2)O results in a progressive increase in wall thickness, eventually causing low compliance. We investigated whether intravesical pressure induces hypertrophy and/or hyperplasia of human bladder smooth muscle cells (HBSMC) mediated by a muscarinic (M) receptor, and evaluated the relationship between intravesical pressure and M receptor antagonists.

MATERIALS AND METHODS

HBSMC were exposed to 40 cmH(2)O pressure and/or acetylcholine (10 nM-100 microM) for 24h. Cells exposed to hydrostatic pressure were treated with either 1 microM AF-DX 16 (M(2) antagonist), 1 microM 4-DAMP (M(3) antagonist) or 1 microM atropine (both M(2) and M(3) antagonists). DNA and protein synthesis of HBSMC were measured by (3)H-thymidine and leucine incorporation assays, respectively.

RESULTS

(3)H-thymidine incorporation increased following exposure to increasing concentrations of acetylcholine (at 100 microM, P<0.05). When cells were exposed to 40 cmH(2)O for 24h, (3)H-thymidine incorporation increased by 31.4%, 33.3% and 39.5% in 1 microM, 10 microM and 100 microM of acetylcholine, respectively. With exposure to 100 microM acetylcholine, a hydrostatic pressure of 40 cm, and both of these together, (3)H-thymidine incorporation increased by 16.7%, 25.9% and 39.4%, respectively, and leucine incorporation increased by 66.5%, 66.5% and 81.8%, respectively (P<0.05). Antimuscarinic agents had no apparent effect on the proliferative rate of cells grown at atmospheric pressure, but there was a dramatic decrease in thymidine and leucine incorporation for cells that were simultaneously exposed to increased hydrostatic pressure, most pronounced when the combined M(2)/M(3) receptor antagonist was applied.

CONCLUSIONS

Intravesical pressure may induce hypertrophy/hyperplasia of HBSMC mediated by M receptors. Early use of an M receptor antagonist in cases of high intravesical pressure may have a positive effect on bladder compliance.

Effect of organophosphorus insecticides and their metabolites on astroglial cell proliferation

Though little attention has been given to the possibility that glial cells may represent a target for the developmental neurotoxicity of organophosphorus (OP) insecticides, recent evidence, obtained in particular with chlorpyrifos (CP), suggests that developmental exposure to this compound may indeed target astrocytes. To substantiate and expand these observations, we carried out a series of in vitro studies utilizing fetal rat astrocytes and a human astrocytoma cell line, 1321N1 cells, to investigate the effect of the OPs CP, diazinon (DZ) and parathion (P), their oxygen analogs chlorpyrifos oxon (CPO), diazoxon (DZO) and paraoxon (PO), and their metabolites 3,5,6-trichloro-2-pyridinol (TCP), 2-isopropyl-6-methyl-4-pyrimidol (IMP) and para-nitrophenol (PNP), on cell proliferation. In fetal rat astrocytes and astrocytoma cells maintained in serum, CP, DZ, P, CPO, DZO, and PO induced a concentration-dependent inhibition in [(3)H]thymidine incorporation with a very similar potency (IC(50) between 45 and 57 microM). Among the other metabolites, PNP was the most potent (IC(50)=70-80 microM), while TCP and IMP were much less effective (IC(50)>100 microM). Cytotoxicity appears to account only for a small part of the effect on DNA synthesis. OP insecticides and their oxons were three- to six-fold more potent in inhibiting [(3)H]thymidine incorporation when cells were synchronized in the G(0)/G(1) phase of the cell cycle and re-stimulated by carbachol or epidermal growth factor. These results suggest that OP insecticides and their oxons affect astroglial cell proliferation and that the transition from the G(0)/G(1) to the S/G(2) phase of the cell cycle may be particularly sensitive to the action of these compounds.

Expression of cholinesterases in brain and non-brain tumours

Although the involvement of cholinesterases (ChEs) in the removal of acetylcholine (ACh) at cholinergic synapses is firmly established, there is evidence to suggest that acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) take part in several cellular processes. The early expression of ChE genes during embryonic development and their role in morphogenesis and apoptosis have been explained on the basis of the non-cholinergic actions of ChEs. In addition, the effects of AChE and BuChE, their inhibitors and antisense oligonucleotides in proliferating cellular systems, together with the mitogenic actions of ACh, support a role for ChEs in cell cycle control. The anomalous expression of ChEs may increase cell proliferation and contribute to cancer growth or development. The aim of this report is to compile the available information on ChEs in cancerous tissues in order to stimulating the research to clarify the molecular mechanisms by which ChEs may participate in cancer. Future investigations may throw light into this intriguing issue which will be of benefit to humankind.

Muscarinic M1 and M3 receptor binding alterations in pancreas during pancreatic regeneration of young rats

The importance of muscarinic receptors in proliferation of different cell types and in insulin secretion from pancreatic beta cells has been extensively studied. However, the role of pancreatic muscarinic receptors during pancreatic regeneration has not yet been studied. For the first time, the functional status of the muscarinic M1 and M3 receptors in regeneration of the pancreas is investigated here. It is observed that the number and affinity of high-affinity muscarinic M3 receptors increased at the time of regeneration. The low-affinity M3 receptors also showed a similar trend. In the case of muscarinic M1 receptors, the receptor number increased with a decrease in affinity. We also observed an increase in the circulating insulin levels at the time of active regeneration. The in vitro studies confirmed that muscarinic receptors are stimulatory to insulin secretion. Our results suggest that the increased muscarinic M1 and M3 receptor subtypes stimulate insulin secretion and islet cell proliferation during the regeneration of pancreas.

Smoking during early pregnancy affects the expression pattern of both nicotinic and muscarinic acetylcholine receptors in human first trimester brainstem and cerebellum

Prenatal nicotine exposure is associated with an increased risk of complications during pregnancy and childhood. In this study the expression of nicotinic and muscarinic acetylcholine receptors in first trimester pons, medulla oblongata and cerebellum from abortus (5-12 weeks of gestation) of smoking and nonsmoking women was compared. A significant age-related increase in binding of nicotinic receptor subtype alpha4 was found in both pons and cerebellum only in fetal tissue from non-smoking women, while a similar increase was observed in medulla oblongata from fetuses exposed to smoking. A significant age-related increase in binding of muscarinic receptor subtype m2 was observed in pons from abortus of smoking compared with non-smoking women. The gene expression pattern of both alpha4 and alpha7 nicotinic receptor subunits was changed after smoking in all three regions investigated. Smoking also changed the expression of m1 and 2 muscarinic receptor mRNA in pons, m1 mRNA in cerebellum and the m3 mRNA in medulla oblongata. The findings indicate that early prenatal nicotine exposure affects the normal developmental pattern of the cholinergic system in human fetal brain.

Continuous ethanol exposure inhibits agonist-stimulated phosphorylation of p70S6 kinase and ribosomal S6 protein in cultured rat astrocytes

The effects of ethanol exposure on agonist-stimulated phosphorylation of p70S6 kinase and ribosomal S6 protein were determined in confluent astrocyte monolayers. Basal phosphorylation of p70S6 kinase and S6 protein was either unaffected or reduced, respectively, after exposure to 50 mM ethanol for 4 days. The abilities of norepinephrine, carbachol and epidermal growth factor to phosphorylate these proteins were significantly decreased after ethanol exposure. In contrast, ethanol exposure had no effect on the protein expression of either p70S6 kinase or S6 protein. Our data suggest that continuous ethanol exposure results in a generalized decrease in agonist-activation of the p70S6 pathway.

Cholinergic modulation of baker's yeast cell phagocytosis by rat astrocytes

Cholinergic regulation of baker's yeast cell phagocytosis in rat cultured astrocytes was studied. Phagocytic activity was reduced by 1 x 10(-5) M of atropine or pirenzepine, but not by AF-DX116 or 4-DAMP. In addition, carbachol stimulated phagocytosis in a dose-dependent manner. Furthermore, only 1 x 10(-5)M of atropine, pirenzepine and 4-DAMP significantly reduced enhanced activity induced by 1 x 10(-7)M carbachol. It was also observed that L-NMMA, staurosporine, or U-73122, reduced phagocytosis activity while TFP failed to do so. Nitrite levels in astrocyte supernatants increased after baker's yeast cells were incorporated to astrocyte cultures, correlating with enhanced phagocytosis induced by carbachol stimulation, and were reduced by 1 x 10(-5) M of atropine, pirenzepine or aminopiridine, but not by AF-DX116 or 4-DAMP. Enhanced NO production triggered by astrocyte phagocytosis may have pathological consequences.

Effects of carbachol on rat Sertoli cell proliferation and muscarinic acetylcholine receptors regulation: an in vitro study

The aim of the present work was to study the effect of muscarinic agonist on cell proliferation and muscarinic acetylcholine receptors (mAChRs) regulation in rat Sertoli cells. Primary cultures of Sertoli cells were obtained from 8-day and 15-day old male Wistar rats. In proliferation assays, [methyl-3H]thymidine incorporation in Sertoli cells from 8-day and 15-day old rats reached a plateau after 60 min of carbachol incubation and decreased after 120 min of agonist incubation. Binding studies with [N-Methyl-3H]scopolamine ([3H]NMS) indicated a rapid loss of cell surface mAChRs when Sertoli cells from 15-day old rats were incubated with carbachol at 35 degrees C for 2 min. This effect was temperature-dependent. When the incubation of the cells was prolonged at 35 degrees C or at 4 degrees C, after the agonist had been washed away, 94% of mAChRs were present in the cell surface after 120 min incubation at 35 degrees C. At 4 degrees C, however, a low percentage of mAChRs was detected in the cell surface. In the presence of cycloheximide, the recycling of mAChRs to the cell surface was not changed, suggesting that the appearance of mAChRs on cell surface was not dependent on de novo receptor synthesis. In conclusion, our studies indicate that the activation of mAChRs may play a role in rat Sertoli cell proliferation. These receptors may be under regulation (internalization and recycling) when cells are exposed to muscarinic cholinergic agonist.

CREB regulates AChE-R-induced proliferation of human glioblastoma cells

The cyclic adenosine monophosphate (AMP) response element-binding protein, CREB, often modulates stress responses. Here, we report that CREB suppresses the glioblastoma proliferative effect of the stress-induced acetylcholinesterase variant, AChE-R. In human U87MG glioblastoma cells, AChE-R formed a triple complex with protein kinase C (PKC) epsilon and the scaffold protein RACK1, enhanced PKCepsilon phosphorylation, and facilitated BrdU incorporation. Either overexpressed CREB, or antisense destruction of AChE-R mRNA, PKC, or protein kinase A (PKA) inhibitors-but not CREB combined with PKC inhibition suppressed-this proliferation, suggesting that CREB's repression of this process involves a PKC-mediated pathway, whereas impaired CREB regulation allows AChE-R-induced, PKA-mediated proliferation of glioblastoma tumors.

Neurological deficits induced by malathion, DEET, and permethrin, alone or in combination in adult rats

Malathion (O,O-dimethyl-S-[1,2-carbethoxyethyl]phosphorodithionate), DEET (N,N-diethyl-m-toluamide), and permethrin [(+/-)-cis/trans-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropane carboxylic acid (3-phenoxyphenyl) methyl ester] are commonly used pesticides. To determine the effects of the dermal application of these chemicals, alone or in combination, the sensorimotor behavior, central cholinergic system, and histopathological alterations were studied in adult male Sprague-Dawley rats following a daily dermal dose of 44.4 mg/kg malathion, 40 mg/kg DEET, and 0.13 mg/kg permethrin, alone and in combination for 30 d. Neurobehavioral evaluations of sensorimotor functions included beam-walking score, beam walk time, inclined plane, and grip response assessments. Twenty-four hours after the last treatment with each chemical alone or in combination all behavioral measures were impaired. The combination of DEET and permethrin, malathion and permethrin, or the three chemicals together resulted in greater impairments in inclined performance than permethrin alone. Only animals treated with a combination of DEET and malathion or with DEET and permethrin exhibited significant increases in plasma butyrlcholinesterase (BChE) activity. Treatment with DEET or permethrin alone, malathion and permethrin, or DEET and permethrin produced significant increases in cortical acetylcholinesterase (AChE) activity. Combinations of malathion and permethrin or of DEET and permethrin produced significant decreases in midbrain AChE activity. Animals treated with DEET alone exhibited a significant increase in cortical m2 muscarinic ACh receptor binding. Quantification of neuron density in the dentate gyrus, CA1 and CA3 subfields of the hippocampus, midbrain, brainstem, and cerebellum revealed significant reductions in the density of surviving neurons with various treatments. These results suggest that exposure to real-life doses of malathion, DEET, and permethrin, alone or in combination, produce no overt signs of neurotoxicity but induce significant neurobehavioral deficits and neuronal degeneration in brain.

Neuroregulation of the neuroendocrine compartment of the liver

Liver progenitor cells as well as hepatic stellate cells have neuroendocrine features. Progenitor cells express chromogranin-A and neural cell adhesion molecule, parathyroid hormone-related peptide, S-100 protein, neurotrophins, and neurotrophin receptors, while hepatic stellate cells express synaptophysin, glial fibrillary acidic protein, neural cell adhesion molecule, nestin, neurotrophins, and their receptors. This phenotype suggests that these cell types form a neuroendocrine compartment of the liver, which could be under the control of the central nervous system. We recently showed that the parasympathetic nervous system promotes progenitor cell expansion after liver injury, since selective vagotomy reduces the number of progenitor cells after chemical injury in the rat. Similarly, after transplantation, which surgically denervates the liver, human livers that develop hepatitis have fewer progenitor cells than native, fully innervated livers with similar degrees of liver injury. There is also accumulating experimental evidence linking the autonomic system, in particular the sympathetic nervous system (SNS), with the pathogenesis of cirrhosis and its complications. Recently, it has been shown that hepatic stellate cells themselves respond to neurotransmitters. Moreover, inhibition of the SNS reduced fibrosis in carbon tetrachloride-induced liver injury. In view of the denervated state of transplanted livers, it is very important to unravel the neural control mechanisms of regeneration and fibrogenesis. Moreover, since there is a shortage of donor organs, a better understanding of the mechanisms of regeneration could have therapeutic possibilities, which could even obviate the need for orthotopic liver transplantation.

Transcription of the M1 muscarinic receptor gene in neurons and neuronal progenitors of the embryonic rat forebrain

Development of the nervous system is accompanied by expansion and differentiation of the neuronal progenitors within the embryonic neuroepithelium. Although the role of growth factors in this process is well documented, there is increasing evidence for a role of neurotransmitters. Acetylcholine is known to exert many actions on developing neural cells, but its potential role in neurogenesis is unclear. Here, we show that the M1 muscarinic acetylcholine receptor is expressed in the neuroepithelium of the rat forebrain, where it is found on both nestin+ progenitor cells and TuJ1+ newly differentiated neurons. Furthermore, transcription is governed, at least in part, by regulatory cis elements that are also responsible for driving transcription in neuroblastoma cells. This represents the first demonstration of M1 receptors on neuronal progenitor cells and supports the notion that M1 muscarinic receptors may play a role in development of the nervous system prior to the onset of synaptogenesis and their subsequent role in neurotransmission.

Nuclear factor kappaB activation by muscarinic receptors in astroglial cells: effect of ethanol

Activation of muscarinic receptors leads to proliferation of astroglial cells and this effect is inhibited by ethanol. Among the intracellular pathways involved in the mitogenic action of muscarinic agonists, activation of the atypical protein kinase C zeta (PKC zeta) appears to be of most importance, and is also affected by low ethanol concentrations. PKC zeta has been reported to activate nuclear factor kappaB (NF-kappaB), a transcription factor that has been shown to play an important role in cell proliferation. The aim of this study was, therefore, to determine whether muscarinic receptors would activate NF-kappaB in astroglial cells, whether such activation would play a role in the mitogenic action of muscarinic agonists, and whether it would represent a possible target for ethanol. Carbachol activated NF-kappaB in human 1321N1 astrocytoma cells, as evidenced by translocation of the p65 subunit of NF-kappaB to the nucleus, phosphorylation and degradation of IkappaBalpha in the cytosol, and increase NF-kappaB binding to DNA. Carbachol also induced translocation of p65 to the nucleus in primary rat astrocytes. Carbachol-induced NF-kappaB activation was mediated by the M3 subtype of muscarinic receptors and appeared to involve Ca(2+) mobilization and activation of PKC epsilon and PKC zeta, but not PI3-kinase and mitogen-activated protein kinase. The NF-kappaB peptide inhibitor SN50, but not the inactive peptide SN50M, strongly inhibited carbachol-induced astrocytoma cells proliferation and p65 translocation to the nucleus. Increased DNA synthesis was also antagonized by the IkappaBalpha kinase inhibitor BAY 11-7082. Ethanol (25-100 mM) inhibited the translocation of p65 and the binding of NF-kappaB to DNA in both 1321N1 astrocytoma cells and primary rat cortical astrocytes. Together, these results suggest that activation of NF-kappaB by muscarinic receptors in astroglial cells is important for carbachol-induced DNA synthesis and that ethanol-mediated inhibition of cell proliferation may be due in part to inhibition of NF-kappaB activation.

Characterization of the effect of Epilobium extracts on human cell proliferation

We have previously shown that extracts of different Epilobium species, a phytotherapeutic agent used in folk medicine as a treatment for benign prostatic hyperplasia, inhibit proliferation of human prostate cells. The selectivity of this effect was evaluated in four different human cell lines (PZ-HPV-7, normal prostate cells; LNCaP, transformed prostate cells; HMEC, mammary cells, and 1321N1, astrocytoma cells). Different extracts of Epilobium species (E. rosmarinifolium, E. spicatum, and E. tetragonum) had similar growth-inhibitory effects in all cell lines tested, indicating a lack of specificity for prostate cells. Inhibition of DNA synthesis was mostly due to the nonpolar fraction of the extracts which is expected to contain flavonoids and sterols. Polar fractions were devoid of activity with the exception of that from E. rosmarinifolium. This species is the most potent in the antiproliferative effect and contains the highest concentration of oenothein B, a hydrolyzable ellagitannin. Oenothein B inhibited DNA synthesis in all four cell lines tested. Extracts of E. angustifolium (the Linné denomination of E. spicatum) and of E. spicatum from different sources were compared for their ability to inhibit DNA synthesis and for their oenothein B content. The E. angustifolium extract contained an amount of oenothein B 40-fold higher than the other extract of the same species and was ten times more potent in inhibiting DNA synthesis in a human prostate cell line. These results indicate that Epilobium extracts inhibit proliferation of prostate cells in a nonspecific manner. Oenothein B may play a role in this effect, but other active compounds are also present. The difference observed between extracts from the same species underscores the importance of determination and standardization of active ingredients in phytotherapeutic agents.

Cytotoxic activity of the root extract from Myoschilos oblongum

The crude methanolic root extract of Myoschilos oblongum exhibited a significant cytotoxic activity against PZ-HPV-7 human prostate cells. Furthermore, two esters of docosanol were isolated from the CH(2)Cl(2) extract.

Ethanol inhibits muscarinic receptor-mediated DNA synthesis and signal transduction in human fetal astrocytes

We previously found that ethanol inhibits muscarinic receptor-induced proliferation of rat cortical astrocytes and human astrocytoma cells and suggested this as a possible mechanism involved in its developmental neurotoxicity. We also observed that, though several signal transduction pathways are relevant for carbachol-induced cell proliferation, activation of PKC zeta and p70S6 kinase is selectively inhibited by low concentrations of ethanol. In the present study we used fetal human astrocytes to expand these findings to a direct target of ethanol in humans. Astrocyte cultures, deriving from legally aborted fetuses, were stained for GFAP and shown to be 90-95% pure. Carbachol induced increases in [(3)H]thymidine and BrdU incorporation in synchronized cells. Carbachol-induced DNA synthesis was strongly inhibited by ethanol. Carbachol also induced phosphorylation of (Thr410)PKC zeta, (Ser473)Akt, and (Thr389)p70S6 kinase, and ethanol (50 mM) inhibited phosphorylation of PKC zeta and p70S6 kinase, but not of Akt. These results expand previous findings in rat astrocytes and human astrocytoma cells and suggest that intracellular signal transduction pathways activated by muscarinic receptors may represent a relevant target for the developmental neurotoxicity of ethanol in humans.

Extracts of various species of Epilobium inhibit proliferation of human prostate cells

This study examined whether various species of Epilobium, a phytotherapeutic agent used in folk medicine as a treatment for benign prostatic hyperplasia, may have an antiproliferative effect in PZ-HPV-7 human prostatic epithelial cells in-vitro. The MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) test, [methyl-(3)H]thymidine incorporation into DNA and flow cytometry analysis were used to evaluate cell proliferation. Ethanolic extracts of E. spicatum, E. rosmarinifolium and E. tetragonum inhibited DNA synthesis in PZ-HPV-7 cells. While at high concentrations all extracts were cytotoxic, DNA synthesis was also decreased at levels that caused no or little cytotoxicity. Treatment of cells with Epilobium extracts did not result in a formation of DNA fragments (evaluated by the TUNEL assay) or chromatin condensation (assessed by Hoechst staining). Flow cytometry analysis indicated that Epilobium extracts inhibit the progression of the cell cycle from the G(0)/G(1) phase. These results suggest that extracts of Epilobium inhibit proliferation of human PZ-HPV-7 cells in-vitro by affecting progression of the cell cycle. This study provides some initial biological plausibility for the use of Epilobium extracts in benign prostatic hyperplasia.

Proliferative effect of acetylcholine on rat trachea epithelial cells is mediated by nicotinic receptors and muscarinic receptors of the M1-subtype

Acetylcholine (ACh), synthesized in mammalian non-neuronal cells such as epithelial cells of the airways, digestive tract and skin, is involved in the regulation of basic cell functions (so-called non-neuronal cholinergic system). In the present experiments rat trachea epithelial cells have been cultured to study the proliferative effect of applied ACh by [3H]thymidine incorporation. ACh (exposure time 24 h) caused a concentration-dependent increase in cell proliferation with a doubling of the [3H]thymidine incorporation at a concentration of 0.1 microM. This effect was partly reduced by 30 microM tubocurarine and completely abolished by the additional application of 1 microM atropine. The stimulatory effect of acetylcholine, remaining in the presence of tubocurarine, was prevented by 1 microM pirenzepine (preferentially acting at M1-receptors), but neither by 1 microM AFDX 116 (preferentially acting at M2-receptors) nor by 1 microM hexahydrosiladifenidol (preferentially acting at M3-receptors). The combination of tubocurarine and pirenzepine halved the basal [3H]thymidine incorporation. In conclusion, ACh produces a proliferative effect in rat trachea epithelial cells, the effect being mediated by both nicotinic receptors and muscarinic receptors of the M1-subtype.

Developmental neurotoxicity of toluene: in vivo and in vitro effects on astroglial cells

Toluene, an inexpensive and available industrial solvent, has become increasingly popular as a drug of abuse. Inhaling toluene leads to a feeling of euphoria and several reports have shown that children born to women who had abused toluene during pregnancy present a syndrome (toluene embryopathy or fetal solvent syndrome) that is characterized by CNS effects (e.g. microencephaly), growth retardation and facial dysmorphologies. The characteristics of the fetal solvent syndrome are very similar to those observed in the fetal alcohol syndrome. As exposure of rats to ethanol during the brain growth spurt has been shown to cause microencephaly and to affect glial cell proliferation and maturation, the present study examines the effects of toluene administration (250, 500 and 750 mg/kg) in neonatal rats from postnatal day 4 to 10. This treatment resulted in a significant decrease in both brain and body weights, and in a significant reduction of levels of glial fibrillary acidic protein, but not of neuron-specific enolase in rat brain. In vitro experiments demonstrate that pharmacologically relevant concentrations of toluene (250-1,000 microM) significantly inhibit proliferation of rat cortical astrocytes without causing overt cytotoxicity. These results indicate that toluene does not cause selective microencephaly; however, it affects brain weight, and appears to target developing astrocytes, possibly by inhibiting their proliferation.

PMA decreases the proliferation of retinal cells in vitro: the involvement of acetylcholine and BDNF

Protein kinase C (PKC) is involved in several cell events including proliferation, survival and differentiation. The aim of this work was to investigate the role of PKC activation on retinal cells proliferation. We demonstrated that PKC activation by phorbol 12-myristate 13-acetate (PMA), a tumor promoter phorbol ester, is able to decrease retinal cells proliferation. This effect was mediated by M1 receptors and dependent on intracellular Ca(2+) increase, tyrosine kinase activity, phosphatidylinositol 3-kinase activity, polypeptide secretion and activation of TrkB receptors. The effect of PMA was not via activation of mitogen-activated protein (MAP) kinase. Carbamylcholine and brain derived neurotrophic factor were both able to decrease retinal cells proliferation to the same level as PMA did. Our results suggest that PKC activation leads to a decrease in retinal cells proliferation through the release of acetylcholine and brain derived neurotrophic factor in the culture, and activation of M1 and TrkB receptors, respectively.

Inhibition of muscarinic receptor-induced proliferation of astroglial cells by ethanol: mechanisms and implications for the fetal alcohol syndrome

In utero exposure to ethanol is deleterious to fetal brain development. Children born with the fetal alcohol syndrome (FAS) display a number of abnormalities, the most significant of which are central nervous system (CNS) dysfunctions, such as microencephaly and mental retardation. An interaction of ethanol with glial cells, particularly astrocytes, has been suggested to contribute to the developmental neurotoxicity of this alcohol. At low concentrations (10-100 mM) ethanol inhibits the proliferation of astroglial cells in vitro, particularly when stimulated by acetycholine through muscarinic M3 receptors. Of the several signal transduction pathways activated by these receptors in astrocytes or astrocytoma cells, which are involved in mitogenic signaling, only some (e.g. protein kinase C (PKC) zeta, p70S6 kinase) appear to be targeted by ethanol at the same low concentrations which effectively inhibit proliferation. Inhibition of astroglial proliferation by ethanol may contribute to the microencephaly seen in FAS.

Aminergic receptors in astrogliotic plaques from patients with multiple sclerosis

Cultured astrocytes express a spectrum of neurotransmitter receptors. However, little is known about these receptors in situ. We previously reported the absence of beta(2) adrenergic receptors on astrocytes in multiple sclerosis (MS). Here we used [(3)H]-radioligands and receptor autoradiography to screen for a variety of other aminergic receptors in six silent chronic astrogliotic plaques in brain tissue obtained from five patients with MS. Dopamine D(1) and histamine H(1) receptors were absent. We detected specific binding for cholinergic muscarinic receptors > dopamine D(2), alpha(1-) and alpha(2)-adrenergic receptors > 5-HT(1A), 5-HT(1B/D), 5-HT(2A), 5-HT(2c), 5-HT(4), and dopamine D(3) receptors. Radiotracers for these aminergic receptors might be useful for studying astrogliosis in patients with MS, and compounds acting at some of these receptors may have potential to modulate astroglial function in MS.

Functional interaction of lithocholic acid conjugates with M3 muscarinic receptors on a human colon cancer cell line

Lithocholic acid (LA) conjugates interact with M3 receptors, the muscarinic receptor subtype that modulates colon cancer cell proliferation. This observation prompted us to examine the action of bile acids on two human colon cancer cell lines: H508, which expresses M3 receptors, and SNU-C4, which does not. Cellular proliferation was determined using a colorimetric assay. Interaction with muscarinic receptors was determined by measuring inhibition of muscarinic radioligand binding and changes in cellular inositol phosphate (IP) formation. Lithocholyltaurine (LCT) caused a dose-dependent increase in H508 cell proliferation that was not observed in SNU-C4 cells. After a 6-day incubation with 300 microM LCT, H508 cell proliferation increased by 200% compared to control. Moreover, in H508 cells, LCT caused a dose-dependent inhibition of radioligand binding and an increase in IP formation. LCT did not alter the rate of apoptosis in H508 or SNU-C4 cells. These data indicate that, at concentrations achievable in the gut, LA derivatives interact with M3 muscarinic receptors on H508 human colon cancer cells, thereby causing an increase in IP formation and cell proliferation. This suggests a mechanism whereby alterations in intestinal bile acids may affect the growth of colon cancer cells.

The vagal nerve stimulates activation of the hepatic progenitor cell compartment via muscarinic acetylcholine receptor type 3

In the rat the hepatic branch of the nervus vagus stimulates proliferation of hepatocytes after partial hepatectomy and growth of bile duct epithelial cells after bile duct ligation. We studied the effect of hepatic vagotomy on the activation of the hepatic progenitor cell compartment in human and rat liver. The number of hepatic progenitor cells and atypical reactive ductular cells in transplanted (denervated) human livers with hepatitis was significantly lower than in innervated matched control livers and the number of oval cells in vagotomized rat livers with galactosamine hepatitis was significantly lower than in livers of sham-operated rats with galactosamine hepatitis. The expression of muscarinic acetylcholine receptors (M1-M5 receptor) was studied by immunohistochemistry and reverse transcriptase-polymerase chain reaction. In human liver, immunoreactivity for M3 receptor was observed in hepatic progenitor cells, atypical reactive ductules, intermediate hepatocyte-like cells, and bile duct epithelial cells. mRNA for the M1-M3 and the M5 receptor, but not the M4 receptor, was detected in human liver homogenates. In conclusion, the hepatic vagus branch stimulates activation of the hepatic progenitor cell compartment in diseased liver, most likely through binding of acetylcholine to the M3 receptor expressed on these cells. These findings may be of clinical importance for patients with a transplant liver.