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Receptor Activation (receptor + activation)
Kinds of Receptor Activation Selected AbstractsSeizure Suppression by Adenosine A1 Receptor Activation in a Mouse Model of Pharmacoresistant EpilepsyEPILEPSIA, Issue 7 2003Nicolette Gouder Summary: Purpose: Because of the high incidence of pharmacoresistance in the treatment of epilepsy (20,30%), alternative treatment strategies are needed. Recently a proof-of-principle for a new therapeutic approach was established by the intraventricular delivery of adenosine released from implants of engineered cells. Adenosine-releasing implants were found to be effective in seizure suppression in a rat model of temporal lobe epilepsy. In the present study, activation of the adenosine system was applied as a possible treatment for pharmacoresistant epilepsy. Methods: A mouse model for drug-resistant mesial temporal lobe epilepsy was used, in which recurrent spontaneous seizure activity was induced by a single intrahippocampal injection of kainic acid (KA; 200 ng in 50 nl). Results: After injection of the selective adenosine A1 -receptor agonist, 2-chloro- N6 -cyclopentyladenosine (CCPA; either 1.5 or 3 mg/kg, i.p.), epileptic discharges determined in EEG recordings were completely suppressed for a period of ,3.5 h after the injections. Seizure suppression was maintained when 8-sulfophenyltheophylline (8-SPT), a non,brain-permeable adenosine-receptor antagonist, was coinjected systemically with CCPA. In contrast, systemic injection of carbamazepine or vehicle alone did not alter the seizure pattern. Conclusions: This study demonstrates that activation of central adenosine A1 receptors leads to the suppression of seizure activity in a mouse model of drug-resistant epilepsy. We conclude that the local delivery of adenosine into the brain is likely to be effective in the control of intractable seizures. [source] Single Chain Variants of the Glycoprotein Hormones and Their Receptors as Tools to Study Receptor Activation and for Analogue DesignJOURNAL OF NEUROENDOCRINOLOGY, Issue 2 2004D. Ben-Menahem Abstract One of the crucial steps in the biosynthesis of multisubunit proteins is their assembly. The glycoprotein hormone, thyroid-stimulating hormone, and the gonadotropins, luteinizing hormone, follicle-stimulating hormone and chorionic gonadotropin, are noncovalent heterodimers. Their assembly is critical for bioactivity because the heterodimers, but not the monomeric subunits, efficiently bind to and activate the cognate heptahelical receptor. Occasionally, mutated subunits cannot combine into a functional hormone, or the bioactivity of the assembled, yet modified, heterodimer is suboptimal. [source] In Vivo Modulation of Post-Spike Excitability in Vasopressin Cells by ,-Opioid Receptor ActivationJOURNAL OF NEUROENDOCRINOLOGY, Issue 8 2000C. H. Brown Abstract An endogenous ,-opioid agonist reduces the duration of phasic bursts in vasopressin cells. Non-synaptic post-spike depolarizing after-potentials underlie activity during bursts by increasing post-spike excitability and ,-receptor activation reduces depolarizing after-potential amplitude in vitro. To investigate the effects of ,-opioids on post-spike excitability in vivo, we analysed extracellular recordings of the spontaneous activity of identified supraoptic nucleus vasopressin cells in urethane-anaesthetized rats infused with Ringer's solution (n = 17) or the ,-agonist, U50,488H (2.5 µg/h at 0.5 µl/h; n = 23), into the supraoptic nucleus over 5 days. We plotted the mean hazard function for the interspike interval distributions as a measure of the post-spike excitability of these cells. Following each spike, the probability of another spike firing in vasopressin cells recorded from U50,488H infused nuclei was markedly reduced compared to Ringer's treated vasopressin cells. To determine whether U50,488H could reduce post-spike excitability in cells that displayed spontaneous phasic activity, we infused U50,488H (50 µg/h at 1 µl/h, i.c.v.), for 1,12 h while recording vasopressin cell activity. Nine of 10 vasopressin cells were silenced by i.c.v. U50,488H 15 ± 5 min into the infusion. Six cells exhibited spontaneous phasic activity before U50,488H infusion and recordings from three of these phasic cells were maintained until activity recovered; during U50,488H infusion, the activity of these three cells was irregular. Generation of the mean hazard function before and during U50,488H infusion revealed a reduction in post-spike excitability during U50,488H infusion. Thus, ,-receptor activation reduces post-spike excitability in vivo; this may reflect inhibition of depolarizing after-potentials and may thus underlie the reduction in burst duration of vasopressin cells caused by an endogenous ,-agonist in vivo. [source] CREB Gene Transcription Factors: Role in Molecular Mechanisms of Alcohol and Drug AddictionALCOHOLISM, Issue 2 2005Subhash C. Pandey This article presents the proceedings of a symposium presented at the meeting of the Research Society on Alcoholism, held in Vancouver, British Columbia, Canada, in June 2004. The organizers and chairpersons were Subhash C. Pandey and Fulton Crews. The presentations were (1) Ethanol Modulation of CREB: Role in Dependence and Withdrawal, by Fulton Crews; (2) Effects of D1 Dopamine Receptor Activation During Withdrawal From Chronic Morphine: Enhanced CREB Activation and Decreased Conditioned Place Aversion, by Elena H. Chartoff; (3) CREB-Haplodeficient Mice: Role in Anxiety and Alcohol-Drinking Behaviors, by Subhash C. Pandey; and (4) A Role for CREB in Stress and Drug Addiction, by Julie A. Blendy. [source] Interactions between Conserved Residues in Transmembrane Helices 2 and 7 during Angiotensin AT1 Receptor ActivationCHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2006Gregory V. Nikiforovich Site-directed mutagenesis studies and independent molecular modeling studies were combined to investigate the network of inter-residue interactions within the transmembrane region of the angiotensin AT1a receptor. Site-directed mutagenesis was focused on residues Tyr292, Asn294, Asn295, and Asn298 in transmembrane helix 7, and the conserved Asp74 in helix 2 and other polar residues. Functional interactions between pairs of residues were evaluated by determining the effects of single and double-reciprocal mutations on agonist-induced AT1a receptor activation. Replacement of Tyr292 by aspartate in helix 7 abolished radioligand binding to both Y292D and D74Y/Y292D mutant receptors. Reciprocal mutations of Asp74/Asn294, Ser115/Asn294, Ser252/Asn294, and Asn298/Sen115 caused additive impairment of function, suggesting that these pairs of residues make independent contributions to AT1a receptor activation. In contrast, mutations of the Asp74/Tyr298 pair revealed that the D74N/N298D reciprocal mutation substantially increased the impaired inositol phosphate responses of the D74N and N298D receptors. Extensive molecular modeling yielded 3D models of the TM region of the AT1 receptor and the mutants as well as of their complexes with angiotensin II, which were used to rationalize the possible reasons of impairing of function of some mutants. These data indicate that Asp74 and Asn298 are not optimally positioned for direct strong interaction in the resting conformation of the AT1a receptor. Balance of interactions between residues in helix 2 (as D74) and helix 7 (as N294, N295 and N298) in the AT1 receptors, however, has a crucial role both in determining their functional activity and levels of their expression. [source] Trafficking of neurokinin receptors: regulation, mechanism and functionEXPERIMENTAL DERMATOLOGY, Issue 9 2004N. Bunnett Cellular responses to agonists of G-protein-coupled receptors (GPCRs) depend in large part on the trafficking of receptors between the plasma membrane and intracellular locations. Receptor activation usually triggers rapid endocytosis of receptors, which either recycle to the cell surface or are targeted for degradation, depending on the receptor in question and the nature of the stimulation. Activation of neurokinin receptors (NKRs) induces membrane translocation of G-protein receptor kinases, which phosphorylate the receptors and ,-arrestins, which interact with phosphorylated receptors. ,-arrestins: 1) uncouple receptors from G-proteins to mediate desensitization; 2) are adaptors for clathrin and AP-2 and mediate clathrin and dynamin-dependent endocytosis of receptors; and 3) interact with components of the MAP kinase pathway such as src, and thereby determine the subcellular location and function of activated MAP kinases. The fate of endocytosed NKRs depends on the receptor and the nature of the stimulus. Transient stimulation with low concentrations of SP (1 nm, 10 min) induces rapid recycling of the NK1R from superficially located endosomes by a mechanism that is mediated by rab4a and rab11a. Higher concentrations of SP (10 nm) induce rab5a-dependent trafficking of the NK1R to perinuclear sorting endosomes and a gradual recycling to the plasma membrane. Continuous stimulation with high concentrations of SP (100 nm, 180 min) induces NK1R ubiquitination and trafficking for degradation. The fate of endocytosed receptors also depends on their interaction with ,-arrestins. The NK1R forms stable high-affinity interactions with both ,-arrestins 1 and 2 at the plasma membrane and in endosomes, whereas the NK3R interacts transiently only with ,-arrestin 2 at the cell surface. The nature of these interactions is specified by domains in the intracellular loop 3 and the carboxyl terminus and determine the rate of recycling and resensitization of these receptors. [source] Bioenergetics of mitochondria in cultured neurons and their role in glutamate excitotoxicityJOURNAL OF NEUROSCIENCE RESEARCH, Issue 15 2007David G. Nicholls Abstract The pathologic activation of NMDA receptors by glutamate is a major contributor to neuronal cell death after stroke. Receptor activation causes a massive influx of calcium into the neuron that is accumulated by the mitochondria. The favored hypothesis is that the calcium loaded mitochondria generate reactive oxygen species that damage and ultimately killed the neuron. In this review this hypothesis is critically re-examined with an emphasis on the role played by deficits in ATP generation. Novel techniques are developed to monitor the bioenergetic status of in situ mitochondria in cultured neurons. Applying these techniques to a model of glutamate excitotoxicity suggests that enhanced reactive oxygen species are a consequence rather than a cause of failed cytoplasmic calcium homeostasis (delayed calcium deregulation, [DCD]), but that prior oxidative damage facilitates DCD by damaging mitochondrial ATP generation. This impacts on current hypotheses relating to the neuroprotective effects of mild mitochondrial uncoupling. © 2007 Wiley-Liss, Inc. [source] Decoding epithelial signals: critical role for the epidermal growth factor receptor in controlling intestinal transport functionACTA PHYSIOLOGICA, Issue 1 2009D. F. McCole Abstract The intestinal epithelium engages in bidirectional transport of fluid and electrolytes to subserve the physiological processes of nutrient digestion and absorption, as well as the elimination of wastes, without excessive losses of bodily fluids that would lead to dehydration. The overall processes of intestinal ion transport, which in turn drive the secretion or absorption of water, are accordingly carefully regulated. We and others have identified the epidermal growth factor receptor (EGFr) as a critical regulator of mammalian intestinal ion transport. In this article, we focus on our studies that have uncovered the intricate signalling mechanisms downstream of EGFr that regulate both chloride secretion and sodium absorption by colonocytes. Emphasis will be placed on the EGFr-associated regulatory pathways that dictate the precise outcome to receptor activation in response to signals that may seem, on their face, to be quite similar if not identical. The concepts to be discussed underlie the ability of the intestinal epithelium to utilize a limited set of signalling effectors to produce a variety of outcomes suitable for varying physiological and pathophysiological demands. Our findings therefore are relevant not only to basic biological principles, but also may ultimately point to new therapeutic targets in intestinal diseases where ion transport is abnormal. [source] EndothelinA (ETA) and ETB receptor-mediated regulation of nitric oxide synthase 1 (NOS1) and NOS3 isoforms in the renal inner medullaACTA PHYSIOLOGICA, Issue 4 2007J. C. Sullivan Abstract Aim:, Our laboratory and others have shown that endothelin (ET)-1 directly stimulates nitric oxide (NO) production in inner medullary collecting duct (IMCD) cells. The goal of this study was to determine which NO synthase (NOS) isoforms in IMCD are sensitive to ET-1, and the role of ETA and ETB receptor activation in vivo and in vitro. Methods:, NOS enzymatic activity and NOS isoform protein expression were examined in cultured IMCD-3 cells and isolated renal inner medulla. ETB receptor-deficient homozygous rats (sl/sl) have elevated levels of circulating ET-1 and lack a functional ETB signalling pathway in kidneys, and furthermore provides a unique model to study ETA receptor signalling in the renal inner medulla in vivo. Results:, Incubation of IMCD-3 cells with exogenous ET-1 (50 nm) resulted in ETA -dependent increased NOS1 protein expression in IMCD-3 cells with no effect on NOS2 or NOS3 expression. ETB receptor antagonism has no effect on NOS expression in IMCD-3 cells. Consistent with in vitro results, cytosolic NOS1 protein expression was significantly greater in the renal inner medulla of sl/sl rats compared with heterozygous (sl/+) controls, with no alteration in NOS3 expression. In contrast to protein expression data, NOS1- and NOS3-specific enzymatic activities decreased in the cytosolic fraction from the renal inner medulla of sl/sl compared with sl/+. Conclusion:, These results provide evidence that both ETA and ETB receptors regulate NOS isoform activity in the renal inner medulla and specifically support the hypothesis that ETA receptor activation increases NOS1 expression. [source] Maspin controls mammary tumor cell migration through inhibiting Rac1 and Cdc42, but not the RhoA GTPaseCYTOSKELETON, Issue 5 2007Heidi Y. Shi Abstract Rac1 and Cdc42 are members of the Rho family of small GTPases that play essential roles in diverse cellular functions, including cell migration. The activities of these Rho family proteins are controlled by growth factor receptor activation and cell-ECM interactions. Here, we show that maspin, a well-documented tumor suppressor gene, also controls cell motility through inhibiting Rac1/Cdc42 activity. Using the GST-PAK and GST-Rho binding protein pull-down assays for GTP-bound Rac1, Cdc42, and RhoA, we showed that treatment of MDA-MB-231 tumor cells with recombinant maspin for a short time period significantly inhibited the activity of Rac1 and Cdc42, but not RhoA. The reactive site loop (RSL) within maspin protein is the functional domain involved in the inhibition. Maspin mutants with the RSL deleted or a point mutation in the RSL region lost their inhibitory activity. We further examined the ability of maspin to inhibit Rac1- and Cdc42-mediated signaling pathways and transcription factors. Treatment of MDA-MB-231 cells with maspin led to the inhibition of JNK kinase activity as assayed by immuno-kinase assays. In addition, the AP-1 transcription activity downstream of JNK kinase pathway was also reduced. Together, we have identified Rac1 and Cdc42 as the downstream targets that mediate the inhibition of mammary tumor cell migration by maspin. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source] Reprogramming of genetic networks during initiation of the Fetal Alcohol Syndrome,DEVELOPMENTAL DYNAMICS, Issue 2 2007Maia L. Green Abstract Fetal Alcohol Spectrum Disorders (FASD) are birth defects that result from maternal alcohol use. We used a non a priori approach to prioritize candidate pathways during alcohol-induced teratogenicity in early mouse embryos. Two C57BL/6 substrains (B6J, B6N) served as the basis for study. Dosing pregnant dams with alcohol (2× 2.9 g/kg ethanol spaced 4 hr on day 8) induced FASD in B6J at a higher incidence than B6N embryos. Counter-exposure to PK11195 (4 mg/kg) significantly protected B6J embryos but slightly promoted FASD in B6N embryos. Microarray transcript profiling was performed on the embryonic headfold 3 hr after the first maternal alcohol injection (GEO data series accession GSE1074). This analysis revealed metabolic and cellular reprogramming that was substrain-specific and/or PK11195-dependent. Mapping ethanol-responsive KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways revealed down-regulation of ribosomal proteins and proteasome, and up-regulation of glycolysis and pentose phosphate pathway in B6N embryos; and significant up-regulation of tight junction, focal adhesion, adherens junction, and regulation of the actin cytoskeleton (and near-significant up-regulation of Wnt signaling and apoptosis) pathways in both substrains. Expression networks constructed computationally from these altered genes identified entry points for EtOH at several hubs (MAPK1, ALDH3A2, CD14, PFKM, TNFRSF1A, RPS6, IGF1, EGFR, PTEN) and for PK11195 at AKT1. Our findings are consistent with the growing view that developmental exposure to alcohol alters common signaling pathways linking receptor activation to cytoskeletal reorganization. The programmatic shift in cell motility and metabolic capacity further implies cell signals and responses that are integrated by the mitochondrial recognition site for PK11195. Developmental Dynamics 236:613,631, 2007. © 2007 Wiley-Liss, Inc. [source] Influx of calcium through L-type calcium channels in early postnatal regulation of chloride transporters in the rat hippocampusDEVELOPMENTAL NEUROBIOLOGY, Issue 13 2009Jennifer G. Bray Abstract During the early postnatal period, GABAB receptor activation facilitates L-type calcium current in rat hippocampus. One developmental process that L-type current may regulate is the change in expression of the K+Cl, co-transporter (KCC2) and N+K+2Cl, co-transporter (NKCC1), which are involved in the maturation of the GABAergic system. The present study investigated the connection between L-type current, GABAB receptors, and expression of chloride transporters during development. The facilitation of L-type current by GABAB receptors is more prominent in the second week of development, with the highest percentage of cells exhibiting facilitation in cultures isolated from 7 day old rats (37.5%). The protein levels of KCC2 and NKCC1 were investigated to determine the developmental timecourse of expression as well as expression following treatment with an L-type channel antagonist and a GABAB receptor agonist. The time course of both chloride transporters in culture mimics that seen in hippocampal tissue isolated from various ages. KCC2 levels increased drastically in the first two postnatal weeks while NKCC1 remained relatively stable, suggesting that the ratio of the chloride transporters is important in mediating the developmental change in chloride reversal potential. Treatment of cultures with the L-type antagonist nimodipine did not affect protein levels of NKCC1, but significantly decreased the upregulation of KCC2 during the first postnatal week. In addition, calcium current facilitation occurs slightly before the large increase in KCC2 expression. These results suggest that the expression of KCC2 is regulated by calcium influx through L-type channels in the early postnatal period in hippocampal neurons. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009 [source] Glutamate drives the touch response through a rostral loop in the spinal cord of zebrafish embryosDEVELOPMENTAL NEUROBIOLOGY, Issue 12 2009Thomas Pietri Abstract Characterizing connectivity in the spinal cord of zebrafish embryos is not only prerequisite to understanding the development of locomotion, but is also necessary for maximizing the potential of genetic studies of circuit formation in this model system. During their first day of development, zebrafish embryos show two simple motor behaviors. First, they coil their trunks spontaneously, and a few hours later they start responding to touch with contralateral coils. These behaviors are contemporaneous until spontaneous coils become infrequent by 30 h. Glutamatergic neurons are distributed throughout the embryonic spinal cord, but their contribution to these early motor behaviors in immature zebrafish is still unclear. We demonstrate that the kinetics of spontaneous coiling and touch-evoked responses show distinct developmental time courses and that the touch response is dependent on AMPA-type glutamate receptor activation. Transection experiments suggest that the circuits required for touch-evoked responses are confined to the spinal cord and that only the most rostral part of the spinal cord is sufficient for triggering the full response. This rostral sensory connection is presumably established via CoPA interneurons, as they project to the rostral spinal cord. Electrophysiological analysis demonstrates that these neurons receive short latency AMPA-type glutamatergic inputs in response to ipsilateral tactile stimuli. We conclude that touch responses in early embryonic zebrafish arise only after glutamatergic synapses connect sensory neurons and interneurons to the contralateral motor network via a rostral loop. This helps define an elementary circuit that is modified by the addition of sensory inputs, resulting in behavioral transformation. © 2009 Wiley Periodicals, Inc. Develop Neurobiol 2009 [source] GABAB receptor expression and function in olfactory receptor neuron axon growthDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2004Catherine A. Priest Abstract Neurotransmitters have been implicated in regulating growth cone motility and guidance in the developing nervous system. Anatomical and electrophysiological studies show the presence of functional GABAB receptors on adult olfactory receptor neuron (ORN) nerve terminals. Using antisera against the GABAB R1a/b receptor isoforms we show that developing mouse olfactory receptor neurons express GABAB receptors from embryonic day 14 through to adulthood. GABAB receptors are present on axon growth cones from both dissociated ORNs and olfactory epithelial explants. Neurons in the olfactory bulb begin to express glutamic acid decarboxylase (GAD), the synthetic enzyme for GABA, from E16 through to adulthood. When dissociated ORNs were cultured in the presence of the GABAB receptor agonists, baclofen or SKF97541, neurite outgrowth was significantly reduced. Concurrent treatment of the neurons with baclofen and the GABAB receptor antagonist CGP54626 prevented the inhibitory effects of baclofen on ORN neurite outgrowth. These results show that growing ORN axons express GABAB receptors and are sensitive to the effects of GABAB receptor activation. Thus, ORNs in vivo may detect GABA release from juxtaglomerular cells as they enter the glomerular layer and use this as a signal to limit their outgrowth and find synaptic targets in regeneration and development. © 2004 Wiley Periodicals, Inc. J Neurobiol 60:154,165, 2004 [source] Interplay of constitutively released nucleotides, nucleotide metabolism, and activity of P2Y receptorsDRUG DEVELOPMENT RESEARCH, Issue 2-3 2001Eduardo R. Lazarowski Abstract At least six mammalian P2Y receptors exist that are specifically activated by ATP, UTP, ADP or UDP. Although the existence of ectoenzymes that rapidly metabolize extracellular nucleotides is well established, the relative flux of ATP and UTP through their extracellular metabolic products remains undefined. In addition, the existence of basal nucleotide release and the contribution of resting levels of ATP and UTP to P2 receptor activation are poorly understood. In the absence of exogenous agonists, an apyrase-sensitive inositol phosphate accumulation was observed in resting 16HBE14o, human bronchial epithelial cells endogenously expressing P2Y receptors and in 1321N1 human astrocytoma cells expressing a recombinant P2Y2 receptor. To test whether nucleotide release may account for basal P2 receptor activities, the rates of extracellular accumulation and metabolism of endogenous ATP were examined with resting 16HBE14o,, C6 rat glioma, and 1321N1 cell cultures. Although extracellular ATP concentrations (1-5 nM) remained unchanged for up to 12 h, [,32P] ATP included in the medium (as a radiotracer) was completely degraded within 120 min, indicating that ATP release balanced ATP hydrolysis. The calculated basal rates of ATP release ranged from 20 to 200 fmol/min per million cells. HPLC analysis during steady state revealed that the gamma-phosphate of ATP was reversibly transferred to species further identified as UTP and GTP, implicating ecto-nucleoside diphosphokinase (NDPK)-catalyzed phosphorylation of endogenous UDP and GDP. At steady state, the final 32P-products of [,32P]ATP metabolism were 32P-orthophosphoric acid and a species further purified and identified as 32P-pyrophosphate. Constitutive nucleotide release balanced by the concerted activities of ecto-ATPase, ecto-ATP pyrophosphatase, and ecto-NDPK may determine the resting levels of extracellular nucleotides and therefore, the basal activity of P2 receptors. Drug Dev. Res. 53:66,71, 2001. © 2001 Wiley-Liss, Inc. [source] Vascular effects of adenosine and its analoguesDRUG DEVELOPMENT RESEARCH, Issue 1-2 2001Debbie Prentice Abstract The main action of adenosine on vascular beds is vasodilation via A2 receptors. In addition, A1 receptors are found in some blood vessels, where they cause contraction. Traditionally, adenosine-induced vasodilation in vitro has been attributed to A2A receptor activation; however, it is now clear that A2B receptors are also involved in the regulation of vascular tone. Endothelium dependence of A2 receptor-mediated responses is variable; in some tissues they are blocked by removal of endothelium and/or inhibition of NO-synthase and in some they are not. In addition to A2 receptor-mediated relaxation, there is much evidence that relaxations to adenosine and some of its analogues can also be mediated by a mechanism which cannot be blocked by adenosine receptor antagonists. There is evidence that these responses are endothelium- and NO-independent and that, under conditions where adenosine is taken up into cells, relaxations to the endogenous ligand are entirely mediated by this mechanism, suggesting it is of physiological significance. Drug Dev. Res. 52:346,349, 2001. © 2001 Wiley-Liss, Inc. [source] Epileptiform synchronization in the cingulate cortexEPILEPSIA, Issue 3 2009Gabriella Panuccio Summary Purpose:, The anterior cingulate cortex (ACC),which plays a role in pain, emotions and behavior,can generate epileptic seizures. To date, little is known on the neuronal mechanisms leading to epileptiform synchronization in this structure. Therefore, we investigated the role of excitatory and inhibitory synaptic transmission in epileptiform activity in this cortical area. In addition, since the ACC presents with a high density of opioid receptors, we studied the effect of opioid agonism on epileptiform synchronization in this brain region. Methods:, We used field and intracellular recordings in conjunction with pharmacological manipulations to characterize the epileptiform activity generated by the rat ACC in a brain slice preparation. Results:, Bath-application of the convulsant 4-aminopyridine (4AP, 50 ,M) induced both brief and prolonged periods of epileptiform synchronization resembling interictal- and ictal-like discharges, respectively. Interictal events could occur more frequently before the onset of ictal activity that was contributed by N -methyl- d -aspartate (NMDA) receptors. Mu-opioid receptor activation abolished 4AP-induced ictal events and markedly reduced the occurrence of the pharmacologically isolated GABAergic synchronous potentials. Ictal discharges were replaced by interictal events during GABAergic antagonism; this GABA-independent activity was influenced by subsequent mu-opioid agonist application. Conclusions:, Our results indicate that both glutamatergic and GABAergic signaling contribute to epileptiform synchronization leading to the generation of electrographic ictal events in the ACC. In addition, mu-opioid receptors appear to modulate both excitatory and inhibitory mechanisms, thus influencing epileptiform synchronization in the ACC. [source] Pregabalin Exerts Oppositional Effects on Different Inhibitory Circuits in Human Motor Cortex: A Double-blind, Placebo-controlled Transcranial Magnetic Stimulation StudyEPILEPSIA, Issue 5 2006Nicolas Lang Summary:,Purpose: To explore acute effects of pregabalin (PGB) on human motor cortex excitability with transcranial magnetic stimulation (TMS). Methods: PGB, 600 mg/day, was orally administered in 19 healthy subjects twice daily in a randomized, double-blind, placebo-controlled crossover design. Several measures of motor cortex excitability were tested with single- and paired-pulse TMS. Results: Mean short-interval intracortical inhibition (SICI) was reduced after PGB (74 ± 7% of unconditioned response) compared with placebo (60 ± 6% of unconditioned response). In contrast, mean long-interval intracortical inhibition (LICI) was increased by PGB (26 ± 4% of unconditioned response) compared with placebo (45 ± 8% of unconditioned response), and mean cortical silent period (CSP) showed an increase from 139 ± 8 ms or 145 ± 8 ms after placebo to 162 ± 7 ms or 161 ± 10 ms after PGB. Motor thresholds, intracortical facilitation, and corticospinal excitability were unaffected. Conclusions: The observed excitability changes with oppositional effects on SICI and LICI or CSP suggest ,-aminobutyric acid (GABA)B -receptor activation. They are markedly distinct from those induced by gabapentin, although both PGB and gabapentin are thought to mediate their function by binding to the ,(2)-, subunit of voltage-gated calcium channels. Conversely, the TMS profile of PGB shows striking similarities with the pattern evoked by the GABA-reuptake inhibitor tiagabine. [source] Pharmacodynamic Analysis of the Interaction between Tiagabine and Midazolam with an Allosteric Model That Incorporates Signal TransductionEPILEPSIA, Issue 3 2003Daniël M. Jonker Summary: ,Purpose: The objective of this study was to characterize quantitatively the pharmacodynamic interaction between midazolam (MDL), an allosteric modulator of the ,-aminobutyric acid subtype A (GABAA) receptor, and tiagabine (TGB), an inhibitor of synaptic GABA uptake. Methods: The in vivo concentration,response relation of TGB was determined through pharmacokinetic/pharmacodynamic (PK/PD) modeling. Rats received a single intravenous dose of 10 mg/kg TGB in the absence and the presence of a steady-state plasma concentration of MDL. The EEG response in the 11.5- to 30-Hz frequency band was used as the pharmacodynamic end point. Results: Infusion of MDL resulted in a mean steady-state plasma concentration of 66 ± 3 ng/ml. A significant pharmacokinetic interaction with TGB was observed. MDL inhibited TGB clearance by 20 ± 7 ml/min/kg from the original value of 89 ± 6 ml/min/kg. However, no changes in plasma protein binding of both drugs were observed. The concentration,EEG relation of TGB was described by the sigmoid- Emax model. The pharmacodynamic parameter estimates of TGB were: Emax = 327 ± 10 ,V, EC50 = 392 ± 20 ng/ml, and nH = 3.1 ± 0.3. These values were not significantly different in the presence of MDL. Factors that may explain the lack of synergism were identified by a mechanism-based interaction model that separates the receptor activation from the signal-transduction process. High efficiency of signal transduction and the presence of a baseline response were shown to diminish the degree of synergism. Conclusions: We conclude that the in vivo pharmacodynamic interaction between MDL and TGB is additive rather than synergistic. This strongly suggests that allosteric modulation of the antiseizure activity of a GAT-1 inhibitor by a benzodiazepine does not offer a therapeutic advantage. [source] Both Fc,RIV and Fc,RIII are essential receptors mediating type II and type III autoimmune responses via FcR,-LAT-dependent generation of C5aEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 12 2009Shahzad N. Syed Abstract Fc,RIV is a relatively new IgG Fc receptor (Fc,R) that is reported to contribute to the pathogenesis of autoimmune diseases, although its specific role in relation to Fc,RIII, complement and IgG2 subclasses remains uncertain. Here we define Fc,RIV on macrophages as a receptor for soluble IgG2a/b complexes but not for cellular bound IgG2a and show that simultaneous activation of Fc,RIV and Fc,RIII is critical to mediate certain type II/III autoimmune responses. Fc,RIII-deficient mice display compensatory enhanced Fc,RIV expression, are protected from lung inflammation after deposition of IgG complexes, and show reduced sensitivity to IgG2a/b-mediated hemolytic anemia, indicating that increased Fc,RIV alone is not sufficient to trigger these diseases in the absence of Fc,RIII. Importantly, however, blockade of Fc,RIV is also effective in inhibiting phagocytosis and cytokine production in IgG2b-induced anemia and acute lung injury, processes that display a further dependence on C5a anaphylatoxin receptor. Using gene deletion and functional inhibition studies, we found that Fc,RIII and Fc,RIV are each essential to trigger an FcR,-linker for activation of T-cell-dependent signal that drives C5a production in the Arthus reaction. Together, the results demonstrate a combined requirement for Fc,RIII and Fc,RIV in autoimmune injury, and identify the linker for activation of T cells adaptor as an integral component of linked Fc,R and C5a anaphylatoxin receptor activation to generate inflammation. [source] Fc, receptor I activation induces leukocyte recruitment and promotes aggravation of glomerulonephritis through the FcR, adaptorEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 4 2007Yutaka Kanamaru Abstract Myeloid cells bear Fc receptors (FcR) that mediate inflammatory signaling through the ITAM-containing FcR, adaptor. They express FcR,-associated Fc,RI, which modulate either activating or inhibitory signaling depending on the type of ligand interaction. The role of Fc,RI, in disease progression remains unknown, notably in IgA nephropathy (IgAN), one of major causes of end-stage renal disease, in which large amounts of circulating IgA-immune complexes (IC) may mediate receptor activation. To analyze the involvement of Fc,RI activation in glomerulonephritis (GN), we generated Tg mice expressing a mutated, signaling-incompetent, human Fc,RIR209L that cannot associate with FcR,. Like Fc,RIwt -Tg mice, they developed mesangial IgA deposits but not macrophage infiltration. Fc,RI activation in Fc,RIwt, but not in Fc,RIR209L, Tg mice resulted in marked inflammation with severe proteinuria and leukocyte infiltration in spontaneous IgAN or anti-glomerular basement membrane Ab-induced GN models. Receptor triggering of syngenically transferred Fc,RIwt Tg macrophages into non-Tg animals induced their recruitment into injured kidneys during GN development. Fc,RIwt cross-linking on macrophages activated MAP kinases and production of TNF-, and MCP-1. Moreover, IgA-IC from IgAN patients activated Fc,RI and induced TNF-, production. Thus, Fc,RI activation mediates GN progression by initiating a cytokine/chemokine cascade that promotes leukocyte recruitment and kidney damage. [source] Constitutive opioid receptor activation: a prerequisite mechanism involved in acute opioid withdrawalADDICTION BIOLOGY, Issue 2 2005E Freye The opioid receptor antagonist naltrexone, which is used in detoxification and rehabilitation programmes in opioid addicts, can precipitate opioid withdrawal symptoms even in patients who have no opioid present. We tested the hypothesis that in order to precipitate withdrawal, opioids need to convert the inactive opioid receptor site via protein kinase C into a constitutively active form on which the antagonist precipitates withdrawal. Acute abstinence symptoms were induced by the potent opioid receptor agonist sufentanil (21?,g/kg), given for 6 days, which was followed by the antagonist naltrexone (20?,g/kg i.v.) in the awake trained canine (n,=,10). Abrupt displacement of opioid binding resulted in acute withdrawal symptoms: increase in blood pressure, heart rate, increase in amplitude height of somatosensory evoked potential, reduced tolerance to colon distention and a significant increase in grading of vegetative variables (restlessness, panting, thrashing of the head, whining, yawning, gnawing, salivation and/or rhinorrhoea, mydriasis, stepping of extremities and vomiting). Following a washout period of 14 days, the same animals were given the highly specific protein kinase C inhibitor H7 (250?,g/kg) prior to the same dosages of sufentanil and naltrexone. Such pretreatment was able to either attenuate or completely abolish the acute withdrawal symptoms. The data suggest that for precipitation of withdrawal, intracellular phosphorylation is a prerequisite in order to activate the opioid ,-receptor. In such a setting, naltrexone acts like an ,inverse agonist? relative to the action of the antagonist on a non-preoccupied receptor site not being exposed previously to a potent opioid agonist. [source] Dissociable effects of cocaine-seeking behavior following D1 receptor activation and blockade within the caudal and rostral basolateral amygdala in ratsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2009Yasmin Mashhoon Abstract Research with dopamine D1 receptor antagonists or neuronal inactivating agents suggests that there is dissociable regulation of cocaine-seeking behavior by the rostral and caudal basolateral amygdala. In the present study, discrete infusions of the D1 receptor agonist SKF 81297 (0.0,0.8 ,g per side) were compared with those of the D1 receptor antagonist SCH 23390 (0.0,2.0 ,g per side) to demonstrate directly the importance of D1 receptor mechanisms within the rostral and caudal basolateral amygdala for their functional heterogeneity in regulating cocaine-seeking behavior. Under a second-order schedule, cocaine-seeking behavior was studied during maintenance (cocaine and cocaine cues present) and reinstatement (only cocaine cues present). Food-maintained responding was used to examine the specificity of maximal behaviorally effective doses of SKF 81297 and SCH 23390. The results demonstrated that the D1 agonist (0.4 or 0.8 ,g) increased and the D1 antagonist (1.0 ,g) decreased cocaine-seeking behavior during maintenance when infused into the caudal but not the rostral basolateral amygdala. Cocaine intake was not affected by the agonist, and was decreased by the antagonist. During reinstatement, the D1 agonist (0.4 ,g) increased and the D1 antagonist (1.0 ,g) decreased cocaine-seeking behavior when infused into the rostral but not the caudal basolateral amygdala. In tests for behavioral specificity, the above effective doses of SKF 81297 and SCH 23390 used in self-administration experiments did not alter food-maintained responding. However, the 2.0-,g dose of SCH 23390 suppressed drug-maintained and food-maintained responding after infusion into both subregions. Collectively, these findings indicate dissociable sensitivity to D1 receptor ligands within the caudal and rostral basolateral amygdala for altering cocaine-seeking behavior under different conditions that model phases of addiction. [source] Concepts of neural nitric oxide-mediated transmissionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2008John Garthwaite Abstract As a chemical transmitter in the mammalian central nervous system, nitric oxide (NO) is still thought a bit of an oddity, yet this role extends back to the beginnings of the evolution of the nervous system, predating many of the more familiar neurotransmitters. During the 20 years since it became known, evidence has accumulated for NO subserving an increasing number of functions in the mammalian central nervous system, as anticipated from the wide distribution of its synthetic and signal transduction machinery within it. This review attempts to probe beneath those functions and consider the cellular and molecular mechanisms through which NO evokes short- and long-term modifications in neural performance. With any transmitter, understanding its receptors is vital for decoding the language of communication. The receptor proteins specialised to detect NO are coupled to cGMP formation and provide an astonishing degree of amplification of even brief, low amplitude NO signals. Emphasis is given to the diverse ways in which NO receptor activation initiates changes in neuronal excitability and synaptic strength by acting at pre- and/or postsynaptic locations. Signalling to non-neuronal cells and an unexpected line of communication between endothelial cells and brain cells are also covered. Viewed from a mechanistic perspective, NO conforms to many of the rules governing more conventional neurotransmission, particularly of the metabotropic type, but stands out as being more economical and versatile, attributes that presumably account for its spectacular evolutionary success. [source] Substance P excites globus pallidus neurons in vivoEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2007Qiao-Ling Cui Abstract Substance P is a member of the neurokinin family. Previous studies have reported the existence of substance P and its high-affinity receptor, neurokinin-1 receptor, in globus pallidus. Employing in vivo extracellular recording combined with behavioural tests, the effects of substance P in globus pallidus of rats were studied. Micropressure ejection of the selective neurokinin-1 receptor agonist [Sar9,Met(O2)11] substance P increased the spontaneous firing rate of pallidal neurons in a concentration-dependent manner, with increases of 27.3% at 0.01, 33.4% at 0.03, 45.5% at 0.1, 38.4% at 0.3 and 36.4% at 1.0 mm. The selective neurokinin-1 receptor antagonist SR140333B prevented the excitatory effects induced by [Sar9,Met(O2)11] substance P. In behaving rats, we observed the postural effects of neurokinin-1 receptor activation in the globus pallidus. Consistent with electrophysiological results, unilateral microinjection of [Sar9,Met(O2)11] substance P (0.1 mm) led to a SR140333B-sensitive contralateral deflection in the presence of systemic haloperidol administration. Combining electrophysiological and behavioural findings, we concluded that substance P produces excitatory effects on globus pallidus neurons via neurokinin-1 receptors. [source] Differential responses to NMDA receptor activation in rat hippocampal interneurons and pyramidal cells may underlie enhanced pyramidal cell vulnerabilityEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2005E. Avignone Abstract Hippocampal interneurons are generally more resistant than pyramidal cells to excitotoxic insults. Because NMDA receptors play a crucial role in neurodegeneration, we have compared the response to exogenous NMDA in CA1 pyramidal cells and interneurons of the stratum oriens using combined whole-cell patch-clamp recording and ratiometric Ca2+ imaging. In voltage-clamp, current-clamp or in nominally Mg2+ -free medium, NMDA (10 µm; 3,5 min exposure in the presence of tetrodotoxin) induced a markedly larger inward current and Ca2+ rise in pyramidal cells than in interneurons. Pyramidal cells also showed a more pronounced voltage dependence in their response to NMDA. We hypothesized that this enhanced response to NMDA receptor activation in pyramidal cells could underlie their increased vulnerability to excitotoxicity. Using loss of dye as an indicator of degenerative membrane disruption, interneurons tolerated continuous exposure to a high concentration of NMDA (30 µm) for longer periods than pyramidal cells. This acute neurodegeneration in pyramidal cells was independent of intracellular Ca2+, because high intracellular BAPTA (20 mm) did not prolong survival time. Thus, a plausible explanation for the enhanced sensitivity of pyramidal neurons to excitotoxic insults associated with cerebral ischemia is their greater response to NMDA receptor activation, which may reflect differences in NMDA receptor expression and/or subunit composition. [source] A role for synGAP in regulating neuronal apoptosisEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2005Irene Knuesel Abstract The brain-specific Ras/Rap GTPase-activating protein synGAP is a major component of the postsynaptic density at glutamatergic synapses. It is a target for phosphorylation by Ca2+/calmodulin-dependent protein kinase II, which up-regulates its GTPase-activating activity. Thus, SynGAP may play an important role in coupling N -methyl- d -aspartate-type glutamate receptor activation to signaling pathways downstream of Ras or Rap. Homozygous deletion of synGAP is lethal within the first few days after birth. Therefore, to study the functions of synGAP, we used the cre/loxP recombination system to produce conditional mice mutants in which gradual loss of synGAP begins at ,,1 week, and usually becomes maximal by 3 weeks, after birth. The resulting phenotypes fall into two groups. In a small group, the level of synGAP protein is reduced to 20,25% of wild type, and they die at 2,3 weeks of age. In a larger group, the levels remain higher than ,,40% of wild type, and they survive and remain healthy. In all mutants, however, an abnormally high number of neurons in the hippocampus and cortex undergo apoptosis, as detected by caspase-3 activation. The effect is cell autonomous, occurring only in neuronal types in which the synGAP gene is eliminated. The level of caspase-3 activation in neurons correlates inversely with the level of synGAP protein measured at 2 and 8 weeks after birth, indicating that neuronal apoptosis is enhanced by reduction of synGAP. These data show that synGAP plays a role in regulation of the onset of apoptotic neuronal death. [source] Presynaptic muscarinic acetylcholine receptors suppress GABAergic synaptic transmission in the intermediate grey layer of mouse superior colliculusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2004Fengxia Li Abstract The intermediate grey layer (the stratum griseum intermediale; SGI) of the superior colliculus (SC) receives cholinergic inputs from the parabrachial region of the brainstem. It has been shown that cholinergic inputs activate nicotinic acetylcholine (nACh) receptors on projection neurons in the SGI. Therefore, it has been suggested that they facilitate the initiation of orienting behaviours. In this study, we investigated the effect of muscarinic acetylcholine (mACh) receptor activation on GABAergic synaptic transmission to SGI neurons using the whole-cell patch-clamp recording technique in slice preparations from mice. The GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) evoked in SGI neurons by focal electrical stimulation were suppressed by bath application of 10 µm muscarine chloride. During muscarine application, both the paired-pulse facilitation index and the coefficient of variation of IPSCs increased; however, the current responses induced by a transient pressure application of 1 mm GABA were not affected by muscarine. Muscarine reduced frequencies of miniature IPSCs (mIPSCs) while the amplitudes of mIPSCs remained unchanged. These results suggestd that mAChR-mediated inhibition of IPSCs was of presynaptic origin. The suppressant effect of muscarine was antagonized by an M1 receptor antagonist, pirenzepine dihydrochloride (1 µm), and a relatively specific M3 receptor antagonist, 4-DAMP methiodide (50 nm). By contrast, an M2 receptor antagonist, methoctramine tetrahydrochloride (10 µm), was ineffective. These results suggest that the cholinergic inputs suppress GABAergic synaptic transmission to the SGI neurons at the presynaptic site via activation of M1 and, possibly, M3 receptors. This may be an additional mechanism by which cholinergic inputs can facilitate tectofugal command generation. [source] Segregation of two endocannabinoid-hydrolyzing enzymes into pre- and postsynaptic compartments in the rat hippocampus, cerebellum and amygdalaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2004A. I. Gulyas Abstract Fatty acid amide hydrolase (FAAH) and monoglyceride lipase (MGL) catalyse the hydrolysis of the endocannabinoids anandamide and 2-arachidonoyl glycerol. We investigated their ultrastructural distribution in brain areas where the localization and effects of cannabinoid receptor activation are known. In the hippocampus, FAAH was present in somata and dendrites of principal cells, but not in interneurons. It was located mostly on the membrane surface of intracellular organelles known to store Ca2+ (e.g. mitochondria, smooth endoplasmic reticulum), less frequently on the somatic or dendritic plasma membrane. MGL immunoreactivity was found in axon terminals of granule cells, CA3 pyramidal cells and some interneurons. In the cerebellum, Purkinje cells and their dendrites are intensively immunoreactive for FAAH, together with a sparse axon plexus at the border of the Purkinje cell/granule cell layers. Immunostaining for MGL was complementary, the axons in the molecular layer were intensively labelled leaving the Purkinje cell dendrites blank. FAAH distribution in the amygdala was similar to that of the CB1 cannabinoid receptor: evident signal in neuronal somata and proximal dendrites in the basolateral nucleus, and hardly any labelling in the central nucleus. MGL staining was restricted to axons in the neuropil, with similar relative signal intensities seen for FAAH in different nuclei. Thus, FAAH is primarily a postsynaptic enzyme, whereas MGL is presynaptic. FAAH is associated with membranes of cytoplasmic organelles. The differential compartmentalization of the two enzymes suggests that anandamide and 2-AG signalling may subserve functional roles that are spatially segregated at least at the stage of metabolism. [source] c-Src kinase activation regulates preprotachykinin gene expression and substance P secretion in rat sensory gangliaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2003Orisa J. Igwe Abstract Increased synthesis of substance P (SP) in the dorsal root ganglia (DRG) and enhanced axonal transport to and secretion from the primary afferent sensory neurons might enhance pain signalling in the spinal dorsal horn by modifying pronociceptive pathways. IL-1, increases SP synthesis by enhancing the expression of preprotachykinin (PPT) mRNA encoding for SP and other tachykinins in the DRG. Stimulation of IL-1 receptor by IL-1, may induce the phosphorylation of tyrosine residues in many effector proteins through the activation of p60c-src kinase. The hypothesis that the synthesis of SP in and secretion from the primary sensory ganglia are regulated by the activation of p60c-src kinase induced by IL-1, was tested. Pretreatment of DRG neurons in culture with herbimycin A, genistein or PP2, three structurally different nonreceptor tyrosine kinase inhibitors that act by different mechanisms, decreased the kinase activity of p60c-src induced by the activation of IL-1 receptor. PP3, a negative control for the Src family of tyrosine kinase inhibitor PP2 had no effect. Herbimycin A and genistein also decreased IL-1,-induced expression of PPT mRNA-encoding transcripts and the levels of SP-li synthesized in the cells and secreted into the culture medium in a concentration-dependent manner. SB 203580 [a p38 mitogen-activated protein kinase (p38 MAPK) inhibitor] and PD 98059 (a p44/42 MAPK kinase inhibitor) were ineffective in modulating IL-1,-induced SP synthesis and secretion, and p60c-src kinase activity in DRG neurons. Whereas, IL-1 receptor antagonist and cycloheximide inhibited IL-1,-evoked secretion of SP-like immunoreactivity (SP-li), actinomycin D decreased it significantly but did not entirely abolish it. These findings show that phosphorylation of specific protein tyrosine residue(s) following IL-1 receptor activation might play a key role in IL-1, signalling to modulate PPT gene expression and SP secretion in sensory neurons. In view of the role of SP as an immunomodulator, these studies provide a new insight into neural-immune intercommunication in pain regulation in the sensory ganglia through the IL-1,-induced p60c-src activation. [source] | |||||||||||||||||||||||||||||||