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Extracellular Concentration (extracellular + concentration)
Selected AbstractsBioreactor Production of Human ,1 -Antitrypsin Using Metabolically Regulated Plant Cell CulturesBIOTECHNOLOGY PROGRESS, Issue 3 2002Melody M. Trexler Transgenic rice cell cultures, capable of producing recombinant human ,1 -antitrypsin (rAAT), were scaled up from shake flasks to a 5-L bioreactor. The maximum specific growth rates (,max) observed from two bioreactor runs were 0.40 day,1 (doubling time of 1.7 days) and 0.47 day,1 (doubling time of 1.5 days), and the maximum specific oxygen uptake rates were 0.78 and 0.84 mmol O2/(g dw h). Using a metabolically regulated rice ,-amylase (RAmy3D) promoter, signal peptide, and terminator, sugar deprivation turned on rAAT expression, and rAAT was secreted into the culture medium. After 1 day of culture in sugar-free medium, there was still continued biomass growth, oxygen consumption, and viability. Extracellular concentrations of 51 and 40 mg active rAAT/L were reached 1.7 and 2.5 days, respectively, after induction in a sugar-free medium. Volumetric productivities for two batch cultures were 7.3 and 4.6 mg rAAT/(L day), and specific productivities were 3.2 and 1.6 mg rAAT/(g dw day). Several different molecular weight bands of immunoreactive rAAT were observed on immunoblots. [source] Evidence for a Role of the Parafascicular Nucleus of the Thalamus in the Control of Epileptic Seizures by the Superior ColliculusEPILEPSIA, Issue 1 2005Karine Nail-Boucherie Summary:,Purpose: The aim of this study was to investigate whether the nucleus parafascicularis (Pf) of the thalamus could be a relay of the control of epileptic seizures by the superior colliculus (SC). The Pf is one of the main ascending projections of the SC, the disinhibition of which has been shown to suppress seizures in different animal models and has been proposed as the main relay of the nigral control of epilepsy. Methods: Rats with genetic absence seizures (generalized absence epilepsy rat from Strasbourg or GAERS) were used in this study. The effect of bilateral microinjection of picrotoxin, a ,-aminobutyric acid (GABA) antagonist, in the SC on the glutamate and GABA extracellular concentration within the Pf was first investigated by using microdialysis. In a second experiment, the effect of direct activation of Pf neurons on the occurrence of absence seizures was examined with microinjection of low doses of kainate, a glutamate agonist. Results: Bilateral injection of picrotoxin (33 pmol/side) in the SC suppressed spike-and-wave discharges for 20 min. This treatment resulted in an increase of glutamate but not GABA levels in the Pf during the same time course. Bilateral injection of kainate (35 pmol/side) into the Pf significantly suppressed spike-and-wave discharges for 20 min, whereas such injections were without effects when at least one site was located outside the Pf. Conclusions: These data suggest that glutamatergic projections to the Pf could be involved in the control of seizures by the SC. Disinhibition of these neurons could lead to seizure suppression and may be involved in the nigral control of epilepsy. [source] PRECLINICAL STUDY: Ghrelin administration into tegmental areas stimulates locomotor activity and increases extracellular concentration of dopamine in the nucleus accumbensADDICTION BIOLOGY, Issue 1 2007Elisabet Jerlhag ABSTRACT Ghrelin stimulates appetite, increases food intake and causes adiposity by mechanisms that include direct actions on the brain. Previously, we showed that intracerebroventricular administration of ghrelin has stimulatory and dopamine-enhancing properties. These effects of ghrelin are mediated via central nicotine receptors, suggesting that ghrelin can activate the acetylcholine,dopamine reward link. This reward link consists of cholinergic input from the laterodorsal tegmental area (LDTg) to the mesolimbic dopamine system that originates in the ventral tegmental area (VTA) and projects to the nucleus accumbens. Given that growth hormone secretagogue receptors (GHSR-1A) are expressed in the VTA and LDTg, brain areas involved in reward, the present series of experiments were undertaken to examine the hypothesis that these regions may mediate the stimulatory and dopamine-enhancing effects of ghrelin, by means of locomotor activity and in vivo microdialysis in freely moving mice. We found that local administration of ghrelin into the VTA (1 µg in 1 µl) induced an increase in locomotor activity and in the extracellular concentration of accumbal dopamine. In addition, local administration of ghrelin into the LDTg (1 µg in 1 µl) caused a locomotor stimulation and an increase in the extracellular levels of accumbal dopamine. Taken together, this indicates that ghrelin might, via activation of GHSR-1A in the VTA and LDTg, stimulate the acetylcholine,dopamine reward link, implicating that ghrelin is a part of the neurochemical overlap between the reward systems and those that regulate energy balance. [source] In vivo voltammetric monitoring of norepinephrine release in the rat ventral bed nucleus of the stria terminalis and anteroventral thalamic nucleusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2009Jinwoo Park Abstract The role and contribution of the dense noradrenergic innervation in the ventral bed nucleus of the stria terminalis (vBNST) and anteroventral thalamic nucleus (AV) to biological function and animal behaviors is poorly understood due to the small size of these nuclei. The aim of this study was to compare norepinephrine release and uptake in the vBNST with that in the AV of anesthetized rats. Measurements were made in vivo with fast-scan cyclic voltammetry following electrical stimulation of noradrenergic projection pathways, either the dorsal noradrenergic bundle (DNB) or the ventral noradrenergic bundle (VNB). The substance detected was identified as norepinephrine based upon voltammetric, anatomical, neurochemical and pharmacological evidence. Fast-scan cyclic voltammetry enables the selective monitoring of local norepinephrine overflow in the vBNST evoked by the stimulation of either the DNB or the VNB while norepinephrine in the AV was only evoked by DNB stimulation. The ,2-adrenoceptor antagonist yohimbine and the norepinephrine uptake inhibitor desipramine increased norepinephrine overflow and slowed its disappearance in both regions. However, control of extracellular norepinephrine by both autoreceptors and uptake was greater in the AV. The greater control exerted by autoreceptors and uptake in the AV resulted in reduced extracellular concentration compared with the v,BNST when large numbers of stimulation pulses were employed. The differences in noradrenergic transmission observed in the terminal fields of the v,BNST and the AV may differentially regulate activity in these two regions that both contain high densities of norepinephrine terminals. [source] Lipophilic cationic drugs increase the permeability of lysosomal membranes in a cell culture system,JOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2010Johannes Kornhuber Lysosomes accumulate many drugs several fold higher compared to their extracellular concentration. This mechanism is believed to be responsible for many pharmacological effects. So far, uptake and release kinetics are largely unknown and interactions between concomitantly administered drugs often provoke mutual interference. In this study, we addressed these questions in a cell culture model. The molecular mechanism for lysosomal uptake kinetics was analyzed by live cell fluorescence microscopy in SY5Y cells using four drugs (amantadine, amitriptyline, cinnarizine, flavoxate) with different physicochemical properties. Drugs with higher lipophilicity accumulated more extensively within lysosomes, whereas a higher pKa value was associated with a more rapid uptake. The drug-induced displacement of LysoTracker was neither caused by elevation of intra-lysosomal pH, nor by increased lysosomal volume. We extended our previously developed numerical single cell model by introducing a dynamic feedback mechanism. The empirical data were in good agreement with the results obtained from the numerical model. The experimental data and results from the numerical model lead to the conclusion that intra-lysosomal accumulation of lipophilic xenobiotics enhances lysosomal membrane permeability. Manipulation of lysosomal membrane permeability might be useful to overcome, for example, multi-drug resistance by altering subcellular drug distribution. J. Cell. Physiol. 224:152,164, 2010 © 2010 Wiley-Liss, Inc. [source] Synthesis of 3H- and 14C-labeled AR-A000002, a new and selective 5-HT1B/1D ligandJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 3 2004Tom Werner Abstract AR-A000002 is a novel and selective high-affinity 5-HT1B/1D receptor antagonist. The compound has been shown to enhance 5-HT turnover in the guinea pig brain in vivo and to increase the extracellular concentration of 5-HT and the metabolite 5-hydroxyindoleacetic acid (5-HIAA) in guinea pig frontal cortex. The observed effects suggest that the compound could be used for the treatment of affective disorders. The syntheses of labeled AR-A000002 analogues as needed for the further pharmacological evaluation of this selective 5-HT1B/1D antagonist, are described. Copyright © 2004 John Wiley & Sons, Ltd. [source] Intermittent Footshock Facilitates Dendritic Vasopressin Release but Suppresses Vasopressin Synthesis within the Rat Supraoptic NucleusJOURNAL OF NEUROENDOCRINOLOGY, Issue 7 2003T. Onaka Abstract Emotional stress inhibits vasopressin release from the pituitary but may facilitate its release from the dendrites in the hypothalamus. We examined effects of intermittently applied footshock upon the amount of vasopressin heteronuclear RNA in the hypothalamus. The footshock decreased plasma vasopressin concentration but increased its extracellular concentration within the supraoptic nucleus. The contents of the vasopressin heteronuclear RNA in the supraoptic nucleus were significantly decreased after the shock. These data suggest that intermittent footshock decreases not only vasopressin release from the axon terminals in the pituitary, but also vasopressin synthesis in the cell bodies in the hypothalamus while the stimulus facilitates vasopressin release from the dendrites in the hypothalamus. The data also suggest differential control of dendritic vasopressin release and synthesis in the hypothalamus. [source] Repeated administration of the selective kappa-opioid receptor agonist U-69593 increases stimulated dopamine extracellular levels in the rat nucleus accumbensJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2006José Antonio Fuentealba Abstract Reinforcing properties of drugs of abuse are reduced by the coadministration of kappa opioid receptor (KOR) agonists. This effect is related to the inhibition of dopamine (DA) release in the nucleus accumbens (NAc) produced by the acute administration of KOR agonists. The present study was undertaken to investigate the in vivo effect of the repeated administration of KOR agonist on extracellular DA levels in the NAc. Rats were injected once daily with the selective KOR agonist U-69593 (0.16,0.32 mg/kg) or vehicle for 4 days. Microdialysis studies assessing extracellular concentration of DA in the NAc under basal and K+ -stimulatory conditions were conducted 1 day later. The microdialysis studies revealed that preexposure to U-69593 had no effect on basal extracellular DA levels but significantly augmented the amount of extracellular DA induced by high K+ compared with vehicle pretreated rats. The D2 receptor agonist quinpirole perfused through the dialysis probe in the NAc, although it produced a significant decrease on basal and K+ -stimulated DA levels in control rats, it did not decrease significantly either basal or K+ -stimulated DA levels in U-69593 preexposed rats. Preexposure to U-69593 did not alter the expression of tyrosine hydroxylase or dopamine transporter in the ventral tegmental area. These results show that repeated administration of U-696593 increases the amount of extracellular DA induced by high K in the NAc, an effect that may be related to decreased D2 autoreceptor function. It is suggested that repeated activation of KOR changes the response status of dopaminergic neurons in the NAc. © 2006 Wiley-Liss, Inc. [source] Effect of Acute Ethanol Administration on the Release of Opioid Peptides From the Midbrain Including the Ventral Tegmental AreaALCOHOLISM, Issue 6 2009Samuel Jarjour Background:, Experimental evidence suggests that ethanol alters the activity of the endogenous opioid peptide systems in a dose and brain-region dependent manner. These alterations may influence the processes of ethanol reward and reinforcement. Thus, it was the objective of this study to investigate the response of the 3 major opioid peptide systems (endorphins, enkephalins, and dynorphins) to acute ethanol administration, at the level of the midbrain including the ventral tegmental area (midbrain/VTA), a region important for drug, including ethanol reinforcement. Methods:, Using the in vivo microdialysis technique coupled with specific solid-phase radioimmunoassay for ,-endorphin, met-enkephalin, and dynorphin A1,8, changes in the extracellular concentration of theses peptides at the level of midbrain/VTA were determined at distinct time points following the administration of 0.0 (saline), 0.8, 1.2, 1.6, 2.0, and 2.4 g ethanol/kg B.Wt. Results:, A biphasic effect of ethanol on ,-endorphin release was found, with low to medium (1.2, 1.6, and 2.0 g) but not high (2.4 g) doses of ethanol, inducing a significant increase in the dialysate content of ,-endorphin. A late increase in the dialysate content of dynorphin A1,8 was observed in response to the 1.2 g ethanol dose. However, none of the ethanol doses tested significantly altered the content of met-enkephalin in the dialysate. Conclusions:, The present findings suggest that the ethanol-induced increase of ,-endorphin release at the level of midbrain/VTA may influence alcohol reinforcement. [source] MicroReview: Competence-induced fratricide in streptococciMOLECULAR MICROBIOLOGY, Issue 6 2007Jean-Pierre Claverys Summary Competence for natural genetic transformation in Streptococcus pneumoniae is controlled by the extracellular concentration of the competence-stimulating peptide (CSP), an exported peptide pheromone. Upon entering the competent state, pneumococci start transcribing a number of CSP-responsive genes, termed the early and late competence (com) genes. Some of the proteins encoded by these com genes are absolutely required for DNA uptake and transformation, but most of them are dispensable. This finding indicates that the majority of CSP-regulated proteins in S. pneumoniae is involved in processes unrelated to natural genetic transformation. Recently, however, it became clear that the biological role of a few of the dispensable proteins might be linked to the transformation process. Although these proteins are not needed for transformation per se, they constitute a killing mechanism that could be used by competent cells to acquire DNA from non-competent pneumococci. This mechanism, termed fratricide, has so far only been described for pneumococci. In this manuscript, we review evidence that suggests the conservation of fratricide as well as the independent evolution of its genetic control and of its effectors in several species of the genus Streptococcus, and discuss its possible biological significance in relation to natural transformation. [source] Quinacrine Enhances Vesicular Stomatitis Virus Inactivation and Diminishes Hemolysis of Dimethylmethylene Blue,phototreated Red Cells,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2002Stephen J. Wagner ABSTRACT Several photodynamic methods for virus inactivation in red blood cell (RBC) suspensions have resulted in unwanted hemolysis during extended 1,6°C storage. To explore the possibility that hemolysis may be mediated by a membrane-bound dye, a molecule similar in structure to yet different in light absorption properties from the photosensitizer was used as an inhibitor for RBC membrane binding in virus photoinactivation and photohemolysis studies. The addition of 500 ,M quinacrine to oxygenated RBC before treatment with 3.6 ,M dimethylmethylene blue (DMMB) and 219 mJ/cm2 red light resulted in an increased extracellular concentration of the sensitizer, increased extracelluar viral inactivation kinetics, and decreased hemolysis during 1,6°C storage without alteration of quinacrine absorption properties. These results collectively suggest that despite its recognized affinity for viral nucleic acid, DMMB also binds to RBC membranes and that the bound dye is, in part, responsible for photoinduced hemolysis. [source] Modeling and optimization of hairy root growth in fed-batch processBIOTECHNOLOGY PROGRESS, Issue 3 2010Francis Mairet Abstract This article proposes a feeding strategy based on a kinetic model to enhance hairy roots growth. A new approach for modeling hairy root growth is used, considering that there is no nutrient limitation thanks to an appropriate feeding, and the intracellular pools are supposed to be always saturated. Thus, the model describes the specific growth rate from extracellular concentration of the major nutrients and nutrient uptakes depend on biomass growth. An optimized feeding strategy was determined thanks to the model to maintain the major nutrient levels at their optimum assuming optimal initial concentrations. The optimal feed rate is computed in open loop using kinetic model prediction or in closed loop using conductivity measurements to estimate biomass growth. Datura innoxia was chosen as the model culture system. Shake flask cultures were used to calibrate the model. Finally, cultures in bioreactor were performed to validate the model and the control laws. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Calcium dobesilate potentiates endothelium-derived hyperpolarizing factor-mediated relaxation of human penile resistance arteriesBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2003Javier Angulo We have evaluated the participation of endothelium-derived hyperpolarizing factor (EDHF) in the endothelium-dependent relaxation of isolated human penile resistance arteries (HPRA) and human corpus cavernosum (HCC) strips. In addition, the effect of the angioprotective agent, calcium dobesilate (DOBE), on the endothelium-dependent relaxation of these tissues was investigated. Combined inhibition of nitric oxide synthase (NOS) and cyclooxygenase (COX) nearly abolished the endothelium-dependent relaxation to acetylcholine (ACh) in HCC, while 60% relaxation of HPRA was observed under these conditions. Endothelium-dependent relaxation of HPRA resistant to NOS and COX inhibition was prevented by raising the extracellular concentration of K+ (35 mM) or by blocking Ca2+ -activated K+ channels, with apamin (APA; 100 nM) and charybdotoxin (CTX; 100 nM), suggesting the involvement of EDHF in these responses. Endothelium-dependent relaxation to ACh was markedly enhanced by DOBE (10 ,M) in HPRA but not in HCC. The potentiating effects of DOBE on ACh-induced responses in HPRA, remained after NOS and COX inhibition, were reduced by inhibition of cytochrome P450 oxygenase with miconazole (0.3 mM) and were abolished by high K+ or a combination of APA and CTX. In vivo, DOBE (10 mg kg,1 i.v.) significantly potentiated the erectile responses to cavernosal nerve stimulation in male rats. EDHF plays an important role in the endothelium-dependent relaxation of HPRA but not in HCC. DOBE significantly improves endothelium-dependent relaxation of HPRA mediated by EDHF and potentiates erectile responses in vivo. Thus, EDHF becomes a new therapeutic target for the treatment of erectile dysfunction (ED) and DOBE could be considered a candidate for oral therapy for ED. British Journal of Pharmacology (2003) 139, 854,862. doi:10.1038/sj.bjp.0705293 [source] Functions of glutamate transporters in cerebellar Purkinje cell synapsesACTA PHYSIOLOGICA, Issue 1 2009Y. Takayasu Abstract Glutamate transporters play a critical role in the maintenance of low extracellular concentrations of glutamate, which prevents the overactivation of post-synaptic glutamate receptors. Four distinct glutamate transporters, GLAST/EAAT1, GLT-1/EAAT2, EAAC1/EAAT3 and EAAT4, are distributed in the molecular layer of the cerebellum, especially near glutamatergic synapses in Purkinje cells (PCs). This review summarizes the current knowledge about the differential roles of these transporters at excitatory synapses of PCs. Data come predominantly from electrophysiological experiments in mutant mice that are deficient in each of these transporter genes. GLAST expressed in Bergmann glia contributes to the clearing of the majority of glutamate that floods out of the synaptic cleft immediately after transmitter release from the climbing fibre (CF) and parallel fibre (PF) terminals. It is indispensable to maintain a one-to-one relationship in synaptic transmission at the CF synapses by preventing transcellular glutamate spillover. GLT-1 plays a similar but minor role in the uptake of glutamate as GLAST. Although the loss of neither GLAST nor GLT-1 affects cerebellar morphology, the deletion of both GLAST and GLT-1 genes causes the death of the mutant animal and hinders the folium formation of the cerebellum. EAAT4 removes the low concentrations of glutamate that escape from uptake by glial transporters, preventing the transmitter from spilling over into neighbouring synapses. It also regulates the activation of metabotropic glutamate receptor 1 (mGluR1) in perisynaptic regions at PF synapses, which in turn affects mGluR1-mediated events including slow EPSCs and long-term depression. No change in synaptic function is detected in mice that are deficient in EAAC1. [source] Role of the astrocytic ETB receptor in the regulation of extracellular endothelin-1 during hypoxiaGLIA, Issue 1 2001Martin Hasselblatt Abstract Astrocytes are known to possess an effective endothelin (ET) eliminatory system which involves astrocytic ETA and ETB receptors and may become particularly relevant under pathophysiological conditions. The present study has therefore been designed to explore the effect of standardized hypoxia on extracellular concentrations of endothelin-1 (ET-1) and on endothelin-converting enzyme (ECE) activity in primary rat astrocytes genetically (sl/sl) or experimentally (dexamethasone) deficient in ETB receptors. The results revealed (1) a hypoxia-mediated decrease of extracellular ET-1 in wildtype astrocytes (+/+) that was not observed in ETB -deficient (sl/sl) cultures; (2) an ET receptor antagonist-induced increase in ET-1 in the media of both genotypes with further elevation upon hypoxia in +/+ cultures only; (3) augmentation of the dexamethasone-induced increase in extracellular ET-1 by hypoxia in +/+, but not in sl/sl cultures; (4) synergistic reduction of ETB gene transcription by hypoxia and dexamethasone; and (5) significant increases in endothelin-converting enzyme activity in the presence of hypoxia. To conclude, hypoxia stimulates astrocytic release of mature ET-1. This stimulation is (over)compensated for by increased ET-1 binding to functional ETB receptors. ETB deficiency, whether genetic or experimentally induced, impairs elimination of extracellular ET-1. GLIA 34:18,26, 2001. © 2001 Wiley-Liss, Inc. [source] Neurochemistry of Trigeminal Activation in an Animal Model of MigraineHEADACHE, Issue 2006Michael L. Oshinsky PhD Research techniques such as electrophysiology, cFos protein expression, and other measurements of neuronal activation provide insights into the pathophysiology of pain processing in migraine, but they do not indicate the specific neurotransmitter systems involved. This paper summarizes data from microdialysis experiments in which changes in the neurochemistry of the trigeminal nucleus caudalis (TNC) were monitored during dural stimulation. Microdialysis allows the measurement of extracellular concentrations of neurotransmitters in a small area of the brain, in vivo, by means of a probe equipped with a semipermeable membrane. Microdialysis enables direct measurement of changes in extracellular concentrations of neurotransmitters in the intact animal over time in response to dural inflammation. Following the activation of the dural nociceptors, changes in the extracellular amino acid neurotransmitters in the deep lamina of the TNC were tracked. A 5-minute application of inflammatory soup when compared with saline to the dura of rats induced a transient decrease in extracellular glutamate in the TNC at approximately 30 minutes postapplication. This short-lived decrease was followed by a continuous increase in extracellular glutamate to a level of approximately 3 times the baseline value at 3 hours after application of the inflammatory soup. The time course of this increase in extracellular glutamate correlated with changes in sensory thresholds on the face of the rat from electrophysiological recordings of secondary sensory neurons in the TNC. No significant differences between the inflammatory soup and saline conditions were observed for extracellular concentrations of aspartate (an excitatory amino acid) or the inhibitory neurotransmitters gamma-aminobutyric acid or glutamine. Results of these experiments support an integral role for glutamate in central sensitization of neurons in the TNC, and suggest an important contribution of glutamate to allodynia and hyperalgia in this animal model of migraine. [source] Effect of antisense oligonucleotide against mouse dentine matrix protein 1 on mineralization ability and calcium ions metabolism in odontoblast-like cell line MDPC-23INTERNATIONAL ENDODONTIC JOURNAL, Issue 7 2006J. L. Pang Abstract Aim, To study the mineralization ability and the dynamic changes of intracellular and extracellular concentrations of calcium ions in the odontoblast-like cell line MDPC-23 affected by antisense oligonucleotide (AS-ODN) against mouse dentine matrix protein 1 (DMP1). Methodology, The expression of DMP1 in MDPC-23 cells was detected by an immunohistochemical method and its blocking outcome by the Western blot method. The alkaline phosphatase (ALP) activity, size and number of mineralized nodules, and the intracellular free ([Ca2+]if), total ([Ca2+]it) and the extracellular ([Ca2+]e) calcium ion concentrations in MDPC-23 cells in the experimental group affected with AS-ODN were compared with those in the control group (paired-samples t -test). Results, Dentine matrix protein 1 was stably expressed in a stable way in MDPC-23 cells; the expression was only just detectable at 12 h and became negative after 24 h affected by AS-ODN. Compared with the control groups, ALP activity of MDPC-23 cells in the AS-ODN group was decreased (P < 0.05), and both the number and size of mineralized nodules were smaller than those in the control group. [Ca2+]if in the AS-ODN group increased and then decreased after 24 h. [Ca2+]it dropped substantially to the lowest point at 24 h (P < 0.01). [Ca2+]e increased before treatment for 24 h and then dropped, however, it was still higher than that of the control group. Conclusions, Antisense oligonucleotide against DMP1 could decrease mineralization ability and affect the intracellular and extracellular concentrations of calcium ions in MDPC-23 cells. This would indicate that DMP1 regulates the metabolism and transportation of calcium ions in odontoblasts, and thus boosts dentine mineralization. [source] The effects of local perfusion of DAMGO on extracellular GABA and glutamate concentrations in the rostral ventromedial medullaJOURNAL OF NEUROCHEMISTRY, Issue 3 2008Raf Jan-Filip Schepers Abstract Electrophysiological data suggest an involvement of rostral ventromedial medulla (RVM) GABA and glutamate (GLU) neurons in morphine analgesia. Direct evidence that extracellular concentrations of GABA or GLU are altered in response to mu opioid receptor (MOP-R) activation is, however, lacking. We used in vivo microdialysis to investigate this issue. Basal GABA overflow increased in response to intra-RVM perfusion of KCl (60 mmol/L). Reverse microdialysis of the MOP-R agonist d -Ala(2),NMePhe(4),Gly-ol(5)]enkephalin (DAMGO) (20,500 ,mol/L) produced a concentration-dependent decrease of RVM GABA overflow. Behavioral testing revealed that concentrations that decreased GABA levels increased thermal withdrawal thresholds. A lower agonist concentration that did not increase GABA failed to alter thermal thresholds. DAMGO did not alter GLU concentrations. However, KCl also failed to modify GLU release. Since rapid, transporter-mediated uptake may mask the detection of changes in GLU release, the selective excitatory amino acid transporter inhibitor pyrrolidine-2,4-dicarboxylic acid (tPDC, 0.6 mmol/L) was added to the perfusion medium for subsequent studies. tPDC increased GLU concentrations, confirming transport inhibition. KCl increased GLU dialysate levels in the presence of tPDC, demonstrating that transport inhibition permits detection of depolarization-evoked GLU overflow. In the presence of tPDC, DAMGO increased GLU overflow in a concentration-dependent manner. These data demonstrate that MOP-R activation decreases GABA and increases GLU release in the RVM. We hypothesize that the opposing effects of MOP-R on GLU and GABA transmission contribute to opiate antinociception. [source] Adenosine in the central nervous system: release mechanisms and extracellular concentrationsJOURNAL OF NEUROCHEMISTRY, Issue 3 2001Serena Latini Adenosine has several functions within the CNS that involve an inhibitory tone of neurotransmission and neuroprotective actions in pathological conditions. The understanding of adenosine production and release in the brain is therefore of fundamental importance and has been extensively studied. Conflicting results are often obtained regarding the cellular source of adenosine, the stimulus that induces release and the mechanism for release, in relation to different experimental approaches used to study adenosine production and release. A neuronal origin of adenosine has been demonstrated through electrophysiological approaches showing that neurones can release significant quantities of adenosine, sufficient to activate adenosine receptors and to modulate synaptic functions. Specific actions of adenosine are mediated by different receptor subtypes (A1, A2A, A2B and A3), which are activated by various ranges of adenosine concentrations. Another important issue is the measurement of adenosine concentrations in the extracellular fluid under different conditions in order to know the degree of receptor stimulation and understand adenosine central actions. For this purpose, several experimental approaches have been used both in vivo and in vitro, which provide an estimation of basal adenosine levels in the range of 50,200 nm. The purpose of this review is to describe pathways of adenosine production and metabolism, and to summarize characteristics of adenosine release in the brain in response to different stimuli. Finally, studies performed to evaluate adenosine concentrations under physiological and hypoxic/ischemic conditions will be described to evaluate the degree of adenosine receptor activation. [source] Melatonin disrupts circadian rhythms of glutamate and GABA in the neostriatum of the awake rat: a microdialysis studyJOURNAL OF PINEAL RESEARCH, Issue 4 2000B. Marquez de Prado The purpose of this study was to investigate possible circadian changes in extracellular concentrations of glutamate (GLU) and ,-aminobutyric acid (GABA), and the influence of melatonin on the levels of these neurotransmitters in the neostriatum of awake rats using in vivo microdialysis. At the same time, the concentrations of the amino acids taurine (TAU), glutamine (GLN) and arginine (ARG), as well as dopamine (DA) and its metabolites 3, 4-dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA), were measured in the extracellular fluid. When dialysates were collected over a 24-hr period (6 hr dark, 12 hr light, 6 hr dark), both GLU and GABA, without the infusion of melatonin, exhibited statistically significant rhythms, with higher levels of these constituents during the dark and lower levels during the day. Perfusion with melatonin (for 19 consecutive hours) prevented the daytime reductions in both GLU and GABA. Of the amino acids measured in the dialysates collected from the neostriatum of non-perfused rats, only ARG exhibited a significant change during the light:dark cycle; again, lowest concentrations were measured during the day. While melatonin perfusion did not statistically significantly influence neostriatal levels of TAU and ARG, GLN levels continued to drop during the infusion of the indoleamine. Dialysate concentrations of DA, DOPAC and HVA exhibited circadian rhythms which were not influenced by melatonin perfusion. The findings indicate there are differential effects of melatonin on extracellular neurotransmitter concentrations in the neostriatum of the awake rat. The results also suggest that the day:night variations in GLU and GABA may relate to daily changes in endogenous melatonin production, while DA and its metabolites are minimally influenced by this secretory product. [source] Attenuation of the Stimulant Response to Ethanol is Associated with Enhanced Ataxia for a GABAA, but not a GABAB, Receptor AgonistALCOHOLISM, Issue 1 2009Sarah E. Holstein Background:, The ,-aminobutyric acid (GABA) system is implicated in the neurobiological actions of ethanol, and pharmacological agents that increase the activity of this system have been proposed as potential treatments for alcohol use disorders. As ethanol has its own GABA mimetic properties, it is critical to determine the mechanism by which GABAergic drugs may reduce the response to ethanol (i.e., via an inhibition or an accentuation of the neurobiological effects of ethanol). Methods:, In this study, we examined the ability of 3 different types of GABAergic compounds, the GABA reuptake inhibitor NO-711, the GABAA receptor agonist muscimol, and the GABAB receptor agonist baclofen, to attenuate the locomotor stimulant response to ethanol in FAST mice, which were selectively bred for extreme sensitivity to ethanol-induced locomotor stimulation. To determine whether these compounds produced a specific reduction in stimulation, their effects on ethanol-induced motor incoordination were also examined. Results:, NO-711, muscimol, and baclofen were all found to potently attenuate the locomotor stimulant response to ethanol in FAST mice. However, both NO-711 and muscimol markedly increased ethanol-induced ataxia, whereas baclofen did not accentuate this response. Conclusions:, These results suggest that pharmacological agents that increase extracellular concentrations of GABA and GABAA receptor activity may attenuate the stimulant effects of ethanol by accentuating its intoxicating and sedative properties. However, selective activation of the GABAB receptor appears to produce a specific attenuation of ethanol-induced stimulation, suggesting that GABAB receptor agonists may hold greater promise as potential pharmacotherapies for alcohol use disorders. [source] Release of ATP in the central nervous system during systemic inflammation: real-time measurement in the hypothalamus of conscious rabbitsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2007Alexander V. Gourine Receptors for extracellular ATP (both ionotropic and metabotropic) are widely expressed in the CNS both in neurones and glia. ATP can modulate neuronal activity in many parts of the brain and contributes to the central nervous control of several physiological functions. Here we show that during the systemic inflammatory response the extracellular concentrations of ATP increase in the anterior hypothalamus and this has a profound effect on the development of the thermoregulatory febrile response. In conscious rabbits we measured ATP release in real time with novel amperometric biosensors and monitored a marked increase in the concentration of ATP (4.0 ± 0.7 ,m) in the anterior hypothalamus in response to intravenous injection of bacterial endotoxin , lipopolysaccharide (LPS). No ATP release was observed in the posterior hypothalamus. The release of ATP coincided with the development of the initial phase of the febrile response, starting 18 ± 2 min and reaching its peak 45 ± 2 min after LPS injection. Application of the ATP receptor antagonists pyridoxal-5,-phosphate-6-azophenyl-2,,4,-disulphonic acid, Brilliant Blue G or periodate oxidized ATP dialdehyde to the site of ATP release in the anterior hypothalamus markedly augmented and prolonged the febrile response. These data indicate that during the development of the systemic inflammation, ATP is released in the anterior hypothalamus to limit the magnitude and duration of fever. This release may also have a profound effect on the hypothalamic control of other physiological functions in which ATP and related purines have been implicated to play modulatory roles, such as food intake, hormone secretion, cardiovascular activity and sleep. [source] ,2 -adrenoceptors are critical for antidepressant treatment of neuropathic pain,ANNALS OF NEUROLOGY, Issue 2 2009Ipek Yalcin PharmD Objective Tricyclic antidepressants (TCAs) are one of the first-line pharmacological treatments against neuropathic pain. TCAs increase the extracellular concentrations of noradrenaline and serotonin by blocking the reuptake transporters of these amines. However, the precise downstream mechanism leading to the therapeutic action remains identified. In this work, we evaluated the role of adrenergic receptors (ARs) in the action of TCAs. Methods We used pharmacological and genetic approaches in mice to study the role of ARs in the antiallodynic action of the TCA nortriptyline. Peripheral neuropathy was induced by the insertion of a polyethylene cuff around the main branch of the sciatic nerve. The specific role of ,2 -AR was evaluated by studying ,2 -AR,/, mice. We used von Frey filaments to assess mechanical allodynia. Results The antiallodynic action of nortriptyline was not affected by cotreatment with the ,2 -AR antagonist yohimbine, the ,1 -AR antagonists atenolol or metoprolol, or the ,3 -AR antagonist SR 59230A. On the contrary, the ,-AR antagonists propranolol or sotalol, the ,1/,2 -AR antagonists alprenolol or pindolol, or the specific ,2 -AR antagonist ICI 118,551 blocked the action of nortriptyline. The effect of nortriptyline was also totally absent in ,2 -AR,deficient mice. Interpretation Stimulation of ,2 -AR is necessary for nortriptyline to exert its antiallodynic action against neuropathic pain. These findings provide new insight into the mechanism by which antidepressants alleviate neuropathic pain. Our results also raise the question of a potential incompatibility between ,-blockers that affect ,2 -AR and antidepressant drugs in patients treated for neuropathic pain. Ann Neurol 2009;65:218,225 [source] | |||||||||||||