Muscarinic Cholinergic Receptors Research Articles

Ultrastructural and hormonal modulations of the thyroid gland following arecoline treatment in albino mice

Arecoline is a plant alkaloid of betel nut Areca catechu. Arecoline has immunosuppressive, hepatotoxic, mutagenic and teratogenic effects, and disturbs some endocrine organs in rats. The objective is to investigate the untoward effects of arecoline on the thyroid gland in mice. Intraperitoneal injection of arecoline (10 mg/kg body weight only once) increased the serum T 3 and T 4 levels and decreased the serum TSH 20, 40 or 60 min after the treatment, with maximum effect at 40 min. Chronic arecoline treatment (10 mg/kg body weight daily for 15 days) caused light microscopic and ultrastructural degenerations of thyro-follicular cells with depletion of T 3 and T 4 levels followed by the elevation of the TSH level. Atropine (arecoline antagonist) injection prevented the changes (hyperactivity) induced by acute (40 min) arecline treatment. Arecoline initially stimulates thyroid activity, and eventually inhibits the activity; atropine prevents thyroid dysfunction induced by arecoline. Arecoline action is mediated probably via muscarinic cholinergic receptor—hypothalamic–pituitary–thyroid axis in mice.

Muscarinic Receptor Stimulation of d-Aspartate Uptake into Human SH-SY5Y Neuroblastoma Cells Is Attenuated by Hypoosmolarity

In addition to its function as an excitatory neurotransmitter, glutamate plays a major role as an osmolyte within the central nervous system (CNS). Accordingly, mechanisms that regulate glutamate release and uptake are of physiological importance not only during conditions in which cell volume remains constant but also when cells are subjected to hypoosmotic stress. In the present study, the ability of muscarinic cholinergic receptors (mAChRs) to regulate the uptake of glutamate (monitored as D-aspartate) into human SH-SY5Y neuroblastoma cells under isotonic or hypotonic conditions has been examined. In isotonic media, agonist activation of mAChRs resulted in a significant increase (250-300% of control) in the uptake of D-aspartate and, concurrently, a cellular redistribution of the excitatory amino acid transporter 3 (EAAT3) to the plasma membrane. mAChR-mediated increases in d-aspartate uptake were potently blocked by the EAAT3 inhibitor l-beta-threo-benzyl-aspartate. In hypotonic media, the ability of mAChR activation to facilitate D-aspartate uptake was significantly attenuated (40-50%), and the cellular distribution of EAAT3 was disrupted. Reduction of mAChR-stimulated D-aspartate uptake under hypoosmotic conditions could be fully reversed upon re-exposure of the cells to isotonic media. Under both isotonic and hypotonic conditions, mAChR-mediated increases in D-aspartate uptake depended on cytoskeletal integrity, protein kinase C and phosphatidylinositol 3-kinase activities, and the availability of intracellular Ca2+. In contrast, dependence on extracellular Ca2+ was observed only under isotonic conditions. The results suggest that, although the uptake of D-aspartate into SH-SY5Y cells is enhanced after mAChR activation, this process is markedly attenuated by hypoosmolarity.

Pharmacotherapy of Major Depressive Disorder: Focus on Desvenlafaxine Succinate

The newest antidepressant, desvenlafaxine (DVS) was approved by the FDA in early 2008 and since then, has been available in the market for general use. DVS is dual acting, a serotonin-norepinepherine reuptake inhibitor (SNRI). Like its parent compound, venlafaxine (VEN), DVS inhibits the neuronal re-uptake of both serotonin and norepinepherine while having minimal affinity for muscarinic cholinergic, H1-histaminergic, alpha1-adrenergic and opioid receptors. DVS is moderately effective for MDD at doses ranging from 100–400 milligrams per day. Its possible advantage is its lower risk of drug-drug interaction. There is no extant evidence that it is especially effective over and above the other existing antidepressants. Its niche will be defined by time but one speculation, given preliminary but un-replicated proof of its efficacy in vasomotor instability in peri-menopause, is that it may have a future utility for depressed women entering menopause.

Effects of cholinergic neuromodulation in the rat dorsal cochlear nucleus: a calcium imaging study performed on brain slices.

Event Abstract Back to Event Effects of cholinergic neuromodulation in the rat dorsal cochlear nucleus: a calcium imaging study performed on brain slices. Aron Koszeghy1*, Balázs Pál1, Géza SzXucs1 and Zoltán Rusznák1 1 University of Debrecen, Institute of Physiology, Hungary In a previous study our laboratory showed that the cholinergic agonist, carbachol increased the spontaneous activity of the giant neurons of the dorsal cochlear nucleus (DCN) with electro physiological technics. The increased activity was partly due to a potassium conductance decrease mediated by M3 and M4 muscarinic cholinergic receptors situated directly on the giant cells. We also observed cholinergic modulational effect on the synaptic inputs of the giant cells. To further investigate this presynaptic effect proposed by the electrophysiological experiments, in this work we used “multy neuronal calcium imaging” on Oregon Green-AM loaded DCN slices. We studied the effect of carbachol on the neurons of DCN in the presence of a glutamatergic, glycinergic and GABA-ergic neurotransmission blocking “cocktail” (NBQX, AP5, strychnine, bicuculline). The effect observed on the neurons - parted from each other by this pharmacological manipulation - is presumably mediated through receptors situated directly on these cells themselves. With this method we observed significant calcium event frequency increase in a number of small cells in the DCN. The average diameter of these carbachol-responding-small-cells was 7.1 micron. It suggests that these cells might be the granule cells of the DCN as they have 6-8 micron soma diameter conventionally. Afterwards also in the presence of the glutamatergic, glycinergic and GABA-ergic neurotransmission blocking “cocktail” we examined whether the effect of carbachol can be prevented with atropine. In the case of eight of nine cells showing activity increase for carbachol, atropin prevented the effect of carbachol. Our results point out a significant cholinerg neuro modulatory effect on some of the small cells of the DCN. According to our experimental procedure this effect seems to be mediated by muscarinic receptors situated directly on these “carbachol-responding” small cells, which might be the granule cells of the DCN. Conference: IBRO International Workshop 2010, Pécs, Hungary, 21 Jan - 23 Jan, 2010. Presentation Type: Poster Presentation Topic: Sensory and motor systems Citation: Koszeghy A, Pál B, SzXucs G and Rusznák Z (2010). Effects of cholinergic neuromodulation in the rat dorsal cochlear nucleus: a calcium imaging study performed on brain slices.. Front. Neurosci. Conference Abstract: IBRO International Workshop 2010. doi: 10.3389/conf.fnins.2010.10.00239 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 May 2010; Published Online: 05 May 2010. * Correspondence: Aron Koszeghy, University of Debrecen, Institute of Physiology, Debrecen, Hungary, aron.koeszeghy@meduniwien.ac.at Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Aron Koszeghy Balázs Pál Géza SzXucs Zoltán Rusznák Google Aron Koszeghy Balázs Pál Géza SzXucs Zoltán Rusznák Google Scholar Aron Koszeghy Balázs Pál Géza SzXucs Zoltán Rusznák PubMed Aron Koszeghy Balázs Pál Géza SzXucs Zoltán Rusznák Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Muscarinic cholinergic receptor antagonists enhanced the expression of CD(8)(+)CD(25)(+)Foxp(3)(+) regulatory T cells in stable COPD patients

to investigate the levels of peripheral CD(8)(+)CD(25)(+)Foxp(3)(+) regulatory T cells (CD(8)(+)CD(25)(+)Treg) in stable chronic obstructive pulmonary disease (COPD) patients, and the effect of muscarinic cholinergic receptor antagonist, tiotropium bromide, on the expression of CD(8)(+)CD(25)(+)Treg. from Oct. 2007 to Mar. 2008, 23 patients with stable moderate to severe COPD received tiotropium bromide inhalation (18 microg daily) for 3 months. Before and after the use of tiotropium bromide, lung function was performed and peripheral vein blood samples were collected from the patient. Lymphocytes were isolated by three-color labeled monoclonal antibodies flow cytometry to detect the quantity and percentage of CD(8)(+)T cell, CD(8)(+)CD(25)(+) T cell, CD(8)(+)CD(25)(+)Treg, CD(4)(+)T cell, CD(4)(+)CD(25)(+) T cell and CD(4)(+)CD(25)(+)Treg, respectively. Paired t test was used for comparison between data before and after treatment. in patients with stable COPD, after tiotropium bromide treatment, the percentage of CD(4)(+) T cells was increased from (28 +/- 10)% to (36 +/- 6)%, and the difference was significant (t = 3.20, P < 0.01). CD(4)(+)CD(25)(+) was decreased from (10 +/- 7)% to (4 +/- 3)% (t = 3.78, P < 0.01), and CD(8)(+)CD(25)(+)Treg was increased from (8 +/- 8)% to (21 +/- 21)% (t = 2.72, P < 0.05). At baseline, CD(8)(+) cells, CD(8)(+)CD(25)(+) cells and CD(4)(+)CD(25)(+)Treg were detectable in the peripheral blood, but no significant changes were observed after treatment. After treatment with tiotropium bromide, the lung function was markedly improved; FEV(1), FEV(1)/Pre%, and FEV(1)/FVC were increased from (1.0 +/- 0.3) L, (35 +/- 10)% and (41 +/- 8)% to (1.1 +/- 0.3) L, (40 +/- 11)% and (45 +/- 11)%, respectively (t = 2.65, 2.56 and 2.37, respectively, all P < 0.05). By linear correlation analysis, the quantity of changes of CD(4)(+) T cells and CD(4)(+)CD(25)(+) T cells were negatively correlated with the rate of change in CD(8)(+)CD(25)(+)Treg (r = -0.61, P < 0.05 and r = -0.72, P < 0.01, respectively). in the peripheral blood of patients with stable COPD, there was expression of CD(8)(+)CD(25)(+)Treg and CD(4)(+)CD(25)(+)Treg. The muscarinic receptor antagonist tiotropium bromide, promoted the amplification of CD(4)(+), inhibited the expression of CD(25)(+), and enhanced the expression of CD(8)(+)Treg, suggesting that muscarinic receptor antagonist tiotropium bromide may possess immunomodulation function.

Oral Dryness and Thirst

Saliva is secreted from the salivary glands, and its production is controlled by the autonomic nervous system. Acetylcholine released by the parasympathetic nervous system stimulates muscarinic receptors and triggers the secretion of serous saliva. We found that intraperitoneally injected pilocarpine, which is known as a cholinergic muscarinic receptor agonist and a sialogue, increases not only saliva secretion but also drinking behavior in rats. This indicates that while pilocarpine increases wetness in the oral cavity, it also evokes the sensation of thirst and elicits water intake. Therefore, the thirst sensation can be evoked independently of oral wetness. Further, we found that nicotine, which is a stimulant of cholinergic nicotinic receptor, evokes the thirst sensation. We demonstrated that thirst was induced both by nicotine acting on nicotinic receptors in the brain and by pilocarpine acting on muscarinic receptors in the brain using behavioral, electrophysiological and molecular biological experiments. In this review, we discuss the relationship between oral dryness and thirst, and the different mechanisms underlying these two phenomena. We propose that while the symptom of xerostomia includes both oral dryness and thirst, it is important to understand that oral dryness and the sensation of thirst are intrinsically different.

The Effect of Autonomic Nerve System on Neurotensin Induced Motility in Isolated, Vascularly Perfused Rat Colon

Background/Aims: Although neurotensin (NT) stimulates colon motility and the passage of intestinal contents, the associated mechanism of action remains unclear. The objective of this study was to investigate the effects of NT on colon motility using isolated rat colon. Methods: Intraluminal pressure was measured at both the proximal and distal portions of the isolated colon. An isolated rat colon was perfused with Krebs solution via the superior mesenteric artery. After stabilization, NT was administered in concentrations of 14, 28, 138 and 276 pM. After pretreatment with phentolamine, propranolol, hexamethonium, atropine or tetrodotoxin, NT was administered at a concentration of 276 pM, and then the intraluminal pressure was monitored. Results: NT significantly increased colon motility at concentrations of 14, 28, 138, and 276 in the proximal colon (25.1±6.5%, 175.4±117.0%, 240.8±115.1% and 252.3±110.6%, respectively) and in the distal colon (35.6±11.8%, 97.5±35.1%, 132.7±36.7% and 212.1±75.2%, respectively). The stimulant effect of NT was more potent in the proximal colon, in a concentration-dependent manner (P<0.05). The stimulant effect of NT was significantly inhibited by atropine at both the proximal and distal colon and by tetrodotoxin at the proximal colon, but not by tetrodotoxin at the distal colon and not by propranolol, phentolamine, or hexamethonium at both the proximal and distal colon. Conclusions: NT increased colon motility at both the proximal and distal portions of the rat colon. The effects were more prominent at the proximal portion. The results of this study suggest that the stimulant action of NT may be mediated by local cholinergic muscarinic receptors. (Intest Res 2010;8:162-171) 󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏󰠏

Intrathecal Huperzine A increases thermal escape latency and decreases flinching behavior in the formalin test in rats

Huperzine A (HupA) is an alkaloid isolated from the Chinese club moss Huperzia serrata and has been used for improving memory, cognitive and behavioral function in patients with Alzheimer's disease in China. It has NMDA antagonist and anticholinesterase activity and has shown anticonvulsant and antinociceptive effects in preliminary studies when administered intraperitoneally to mice. To better characterize the antinociceptive effects of HupA at the spinal level, Holtzman rats were implanted with intrathecal catheters to measure thermal escape latency using Hargreaves thermal escape testing system and flinching behavior using the formalin test. Intrathecal (IT) administration of HupA showed a dose-dependent increase in thermal escape latency with an ED50 of 0.57 μg. Atropine reversed the increase in thermal escape latency produced by 10 μg HupA, indicating an antinociceptive mechanism through muscarinic cholinergic receptors. The formalin test showed that HupA decreased flinching behavior in a dose-dependent manner. Atropine also reversed the decrease in flinching behavior caused by 10 μg HupA. A dose-dependent increase of side effects including scratching, biting, and chewing tails was observed, although antinociceptive effects were observed in doses that did not produce any adverse effects.

Attenuation of Cocaine's Reinforcing and Discriminative Stimulus Effects via Muscarinic M1 Acetylcholine Receptor Stimulation

Muscarinic cholinergic receptors modulate dopaminergic function in brain pathways thought to mediate cocaine's abuse-related effects. Here, we sought to confirm and extend in the mouse species findings that nonselective muscarinic receptor antagonists can enhance cocaine's discriminative stimulus. More importantly, we tested the hypothesis that muscarinic receptor agonists with varied receptor subtype selectivity can blunt cocaine's discriminative stimulus and reinforcing effects; we hypothesized a critical role for the M(1) and/or M(4) receptor subtypes in this modulation. Mice were trained to discriminate cocaine from saline, or to self-administer intravenous cocaine chronically. The nonselective muscarinic antagonists scopolamine and methylscopolamine, the nonselective muscarinic agonists oxotremorine and pilocarpine, the M(1)/M(4)-preferring agonist xanomeline, the putative M(1)-selective agonist (4-hydroxy-2-butynyl)-1-trimethylammonium-3-chlorocarbanilate chloride (McN-A-343), and the novel M(1)-selective agonist 1-(1-2-methylbenzyl)-1,4-bipiperidin-4-yl)-1H benzo[d]imidazol-2(3H)-one (TBPB) were tested as substitution and/or pretreatment to cocaine. Both muscarinic antagonists partially substituted for cocaine and enhanced its discriminative stimulus. Conversely, muscarinic agonists blunted cocaine discrimination and abolished cocaine self-administration with varying effects on food-maintained behavior. Specifically, increasing selectivity for the M(1) subtype (oxotremorine < xanomeline < TBPB) conferred lesser nonspecific rate-suppressing effects, with no rate suppression for TBPB. In mutant mice lacking M(1) and M(4) receptors, xanomeline failed to diminish cocaine discrimination while rate-decreasing effects were intact. Our data suggest that central M(1) receptor activation attenuates cocaine's abuse-related effects, whereas non-M(1)/M(4) receptors probably contribute to undesirable effects of muscarinic stimulation. These data provide the first demonstration of anticocaine effects of systemically applied, M(1) receptor agonists and suggest the possibility of a new approach to pharmacotherapy for cocaine addiction.

Oxybutynin chloride topical gel: a new formulation of an established antimuscarinic therapy for overactive bladder

Background: Oxybutynin, a cholinergic-muscarinic receptor antagonist, is established as a safe and effective pharmacological treatment for patients with overactive bladder syndrome (OAB). Oxybutynin is available in multiple immediate- and extended-release oral and two transdermal formulations. Oxybutynin chloride topical gel (OTG) (Gelnique®, Watson Pharmaceuticals, Corona, CA, USA) was approved in January 2009 by the US FDA. OTG was designed to provide consistent plasma oxybutynin levels with daily application, favorably altering the circulating N-desethyloxybutynin metabolite:oxybutynin ratio, and to utilize a biocompatible delivery system, thus minimizing both the anticholinergic adverse effects of oral formulations and the application-site skin reactions associated with other available forms of transdermal delivery. Objective/methods: This review summarizes the pharmacological properties and the clinical efficacy and safety profile of OTG based on the published literature and unpublished data provided by the manufacturer upon request. Results/conclusion: OTG represents an efficacious, safe, and convenient alternative to other oxybutynin formulations and other oral anticholinergic medications for the treatment of OAB. Future studies and broad clinical experience should confirm the promising early experience observed with this formulation.

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 (~35%) and l-MR (~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.

Repeated effects of asenapine on adrenergic and cholinergic muscarinic receptors

Adrenergic (alpha1 and alpha2) and cholinergic muscarinic (M1-M5) receptor binding in rat forebrain was quantified after 4 wk of twice-daily subcutaneous administration of asenapine or vehicle. Asenapine (0.03, 0.1, and 0.3 mg/kg) produced increases in [3H]prazosin binding to alpha1-adrenergic receptors in the medial prefrontal cortex (mPFC: 30%, 39%, 57%) and dorsolateral frontal cortex (DFC: 27%, 37%, 53%) and increased [3H]RX821002 binding to alpha2-adrenergic receptors in mPFC (36%, 43%, 50%) and DFC (41%, 44%, 52%). Despite showing no appreciable affinity for muscarinic receptors, asenapine produced regionally selective increases in binding of [3H]QNB to M1-M5 receptors in mPFC (26%, 31%, 43%), DFC (27%, 34%, 41%), and hippocampal CA1 (40%, 44%, 42%) and CA3 (25%, 52%, 48%) regions. These regionally selective effects of asenapine on adrenergic and cholinergic muscarinic receptor subtypes may contribute to its beneficial clinical effects in the treatment of schizophrenia and bipolar disorder.

Muscimol, AP5, or scopolamine infused into perirhinal cortex impairs two-choice visual discrimination learning in rats

The perirhinal cortex (PRh) has been strongly implicated in object recognition memory and visual stimulus representation. Studies of object recognition have revealed evidence for the involvement of several neurotransmitter subsystems, including those involving NMDA ( N-methyl- d-aspartic acid) and muscarinic cholinergic receptors. In the present study, we assessed the possible involvement of PRh and related receptor subsystems in two-choice visual discrimination learning by Lister Hooded rats tested in touchscreen-equipped operant boxes. In Experiment 1, daily pre-training inactivation of PRh with the GABA A receptor agonist muscimol (0.5 μg/hemisphere) significantly impaired acquisition of the two-choice visual discrimination. In Experiment 2, daily pre-training blockade of either NMDA or muscarinic receptors in PRh with AP5 (5.9 μg/hemisphere) or scopolamine (10 μg/hemisphere), respectively, impaired task acquisition. These results parallel the findings from object recognition studies and suggest a generality of neurotransmitter receptor involvement underlying the role of PRh in both object recognition memory and visual discrimination learning. The involvement of PRh in both types of tasks may be related to its role in complex visual stimulus representation.

Determination of the vectorelectrogram in isolated rat atria: application to the study of arrhythmias

Atrial tachyarrhythmias, the most frequent type of cardiac arrhythmia, are associated with increased stroke risk. Reentry and focal activity are considered as the main mechanisms underlying this dysfunction. In this study, we describe determination of the vectorelectrogram in isolated rat atria as a means to distinguish different patterns of electrical propagation. In all studied right atria beating at sinus rhythm, the mean electric vector (MEV) trajectory was clockwise, and each cycle was preceded by electric diastole (null MEV), either in the absence or presence of muscarinic cholinergic or β-adrenergic receptor stimulation. During cholinergic tachyarrhythmia (induced by high-rate electric stimulation in both atria, plus exposure to carbachol in left atria), vector loops were ellipsoidal and stable, with variable direction, and did not cross the origin, which is consistent with reentrant activation and with findings obtained in vivo by other authors. In contrast, during spontaneous activity induced by rapid pacing in isoproterenol-exposed left atria, vector loops were similar to those in right atria at sinus rhythm, thus suggestive of focal activity. It is concluded that the vectorelectrogram approach allows discrimination of different patterns of propagation during arrhythmia in isolated atria and may be useful for high-output tests of pro- and anti-arrhythmic compounds.

Phosphatidic acid potentiates Gα q stimulation of phospholipase C-β 1 signaling

Phosphatidic acid (PA) is interactive with Gα q-linked agonists to stimulate GPCR signaling via phospholipase C-β 1 (PLC-β 1). Phorbol 12-myristate 13-acetate (PMA) increases cellular levels of PA and phospholipase D activity (PLD). This study evaluated whether PMA can stimulate PLC-β 1 activity via PA, independent of GPCR input in transfected COS 7 cells. PMA alone had little effect on PLC activity in cells co-transfected with PLC-β 1 and Gα q. Activated Gα q, induced by co-transfecting muscarinic cholinergic receptor (m1R), was necessary for stimulation of PLC-β 1 activity by PMA. Stimulation by PMA was dependent on the PA-regulatory motif of PLC-β 1 implicating PA in this mechanism. PLD1 knockdown by antisense decreased responsiveness of PLC-β 1 to both PMA and carbachol. PA alone thus has little effect on PLC-β 1 activity, but PA and PLD1 synergize with activated Gα q to stimulate PLC-β 1 signaling. Coordinate interaction with activated Gα q may serve as an important mechanism to fine tune response to ligands while preventing spurious initiation of PLC-β signaling by PA in cells.

STIM1 Is a Calcium Sensor Specialized for Digital Signaling

When cells are activated by calcium-mobilizing agonists at low, physiological concentrations, the resulting calcium signals generally take the form of repetitive regenerative discharges of stored calcium, termed calcium oscillations [1]. These intracellular calcium oscillations have long fascinated biologists as a mode of digitized intracellular signaling. Recent work has highlighted the role of calcium influx as an essential component of calcium oscillations [2]. This influx occurs through a process known as store-operated calcium entry, which is initiated by calcium sensor proteins, STIM1 and STIM2, in the endoplasmic reticulum [3]. STIM2 is activated by changes in endoplasmic reticulum calcium near the resting level, whereas a threshold of calcium depletion is required for STIM1 activation [4]. Here we show that, surprisingly, it is STIM1 and not STIM2 that is exclusively involved in calcium entry during calcium oscillations. The implication is that each oscillation produces a transient drop in endoplasmic reticulum calcium and that this drop is sufficient to transiently activate STIM1. This transient activation of STIM1 can be observed in some cells by total internal reflection fluorescence microscopy. This arrangement nicely provides a clearly defined and unambiguous signaling system, translating a digital calcium release signal into calcium influx that can signal to downstream effectors.

Promising multifunctional anti-Alzheimer's dimer bis(7)-Cognitin acting as an activator of protein kinase C regulates activities of α-secretase and BACE-1 concurrently

We have recently demonstrated that bis(7)-Cognitin, a promising multifunctional anti-Alzheimer 's dimer, can remarkably reduce the generation of amyloid β peptide (Aβ) by inhibiting β-secretase (BACE-1) and activating α-secretase activity. In this study, the mechanism(s) underlying bis(7)-Cognitin 's regulation of the activity of these two proteases was further investigated. In N2a cells stably expressing human amyloid precursor protein with the Swedish mutation (APPswe), the reduction in Aβ production induced by 1 μM bis(7)-Cognitin was not altered by the co-pretreatment of muscarinic and nicotinic cholinergic receptor antagonists, indicating that the regulation of APP processing by this dimer is independent of cholinergic transmission. Furthermore, bis(7)-Cognitin (0.1–3 μM) significantly increased protein kinase C (PKC) activity in cells and in vitro in a concentration-dependent manner. Administration of a PKC activator, phorbol 12-myristate 13-acetate (PMA), concentration-dependently increased the α-secretase cleavage products, and reduced the BACE-1 cleavage products. In addition, the inhibition of PKC prevented PMA- or bis(7)-Cognitin-induced alterations in α-secretase and BACE-1 activities, eliminating reductions in Aβ production seen with PMA or the dimer. These results strongly suggest that bis(7)-Cognitin may reduce the biosynthesis of Aβ by inhibiting BACE-1 and activating α-secretase concurrently through the direct activation of PKC. Combined with previous findings of direct inhibition of AChE and BACE-1 by this dimer, this work indicates that strategy may have potential to provide new insights into designing novel drugs that target multiple steps of aberrant APP processing to treat Alzheimer 's disease.

TRPC Channels Mediate a Muscarinic Receptor-Induced Afterdepolarization in Cerebral Cortex

Activation of muscarinic cholinergic receptors on pyramidal cells of the cerebral cortex induces the appearance of a slow afterdepolarization that can sustain autonomous spiking after a brief excitatory stimulus. Accordingly, this phenomenon has been hypothesized to allow for the transient storage of memory traces in neuronal networks. Here we investigated the molecular basis underlying the muscarinic receptor-induced afterdepolarization using molecular biological and electrophysiological strategies. We find that the ability of muscarinic receptors to induce the inward aftercurrent underlying the slow afterdepolarization is inhibited by expression of a Galpha(q-11) dominant negative and is also markedly reduced in a phospholipase C beta1 (PLCbeta1) knock-out mouse. Furthermore, we show, using a genetically encoded biosensor, that activation of muscarinic receptor induces the breakdown of phosphatidylinositol 4,5-bisphosphate in pyramidal cells. These results indicate that the Galpha(q-11)/PLCbeta1 cascade plays a key role in the ability of muscarinic receptors to signal the inward aftercurrent. We have shown previously that the muscarinic afterdepolarization is mediated by a calcium-activated nonselective cation current, suggesting the possible involvement of TRPC channels. We find that expression of a TRPC dominant negative inhibits, and overexpression of wild-type TRPC5 or TRPC6 enhances, the amplitude of the muscarinic receptor-induced inward aftercurrent. Furthermore, we find that coexpression of TRPC5 and T-type calcium channels is sufficient to reconstitute a muscarinic receptor-activated inward aftercurrent in human embryonic kidney HEK-293 cells. These results indicate that TRPC channels mediate the muscarinic receptor-induced slow afterdepolarization seen in pyramidal cells of the cerebral cortex and suggest a possible role for TRPC channels in mnemonic processes.

Involvement of vasoactive intestinal polypeptide in the parasympathetic vasodilatation of the rat masseter muscle

The parasympathetic vasodilatory fibres are known to innervate vessels in a rat masseter muscle via both cholinergic and non-cholinergic mechanisms. However, the non-cholinergic mechanisms are still unclear. Recently, vasoactive intestinal polypeptide (VIP) was convincingly shown to be involved in the parasympathetic vasodilatation in orofacial areas, such as submandibular glands and lower lip. However, very little is known about the rat masseter muscle. The present study was designed in the rat masseter muscle to assess (1) whether the parasympathetic nerve innervating vessels have VIP immunoreactivities, (2) whether intravenous administration of VIP induces the vasodilatation, and (3) effects of selective VIP receptor antagonist ([4Cl- d-Phe 6, Leu 17] VIP) in the presence or absence of atropine on the parasympathetic vasodilatation. The VIP immunoreactivities were found at two sites of the parasympathetic otic ganglion and nerve fibres located around vessels. The intravenous administration of VIP induced the vasodilatation, and [4Cl- d-Phe 6, Leu 17] VIP markedly decreased the vasodilatation evoked by VIP administration. The parasympathetic vasodilatation was not inhibited by [4Cl- d-Phe 6, Leu 17] VIP. However, treatment with [4Cl- d-Phe 6, Leu 17] VIP markedly decreased the parasympathetic vasodilatation when [4Cl- d-Phe 6, Leu 17] VIP was administered together with atropine. These results suggest that (1) VIP exists in the postganglionic parasympathetic nerve innervating the vessels in the masseter muscle, (2) the intravenous administration of VIP induces the vasodilatation in the masseter muscle, and (3) VIP may be involved in the parasympathetic vasodilatation in the masseter muscle when muscarinic cholinergic receptors are deactivated by either atropine or the suppression of the ACh release.

Une nouvelle approche de la prise en charge de la schizophrénie : les agonistes partiels des récepteurs D2 de la dopamine

Since chlorpromazine was described, antischizophrenic therapeutics have been enriched with various other D2 dopamine receptors antagonists, either neuroleptics (which develop extrapyramidal side effects) or non neuroleptic antipsychotics (devoid of extrapyramidal side effects when used at effective doses against psychotic expressions). The latter drugs display such properties on account of several associated pharmacological activities (D3 receptors antagonism more efficient than D2 antagonism; antagonism at cholinergic muscarinic receptors; antagonism at 5HT2 serotonin receptors). All these antipsychotic drugs are not, as initially described, neutral antagonists of D2 receptors, but are in fact inverse agonists (alpha<0), because they suppress the constitutive activity of these receptors (i.e. their spontaneous activity in the absence of dopamine stimulation). Thus they induce effects which are opposite to those of dopamine. Partial agonists, also called agonists-antagonists, induce intermediate effects between those of full agonists and neutral antagonists. Their intrinsic activity is the following (1>alpha>0>- 1) in the hierarchy: full agonist>partial agonist>neutral antagonist>inverse agonist. These partial agonists moderate the activity of hyperactive dopaminergic neurons (reducing positive expressions: delusion, hallucinations, agitation). They activate deficient dopaminergic transmissions, alleviating at least partly negative expressions. This approach is presently illustrated by aripiprazole: OP 4597. Many other molecules are candidates for such a therapeutic promotion, justified by the search for both antiproductive and antideficit activities, with a low incidence of adverse side effects such as extrapyramidal effects, thermoregulation effects, induction of late dyskinesias, sedation, bulimia, excessive weight, depressive symptoms, incitation to consume addictive drugs, hyperprolactinemia....