Extracellular Neurotransmitter Levels Research Articles

Real-time monitoring of electrically evoked catecholamine signals in the songbird striatum using in vivo fast-scan cyclic voltammetry

Fast-scan cyclic voltammetry is a powerful technique for monitoring rapid changes in extracellular neurotransmitter levels in the brain. In vivo fast-scan cyclic voltammetry has been used extensively in mammalian models to characterize dopamine signals in both anesthetized and awake preparations, but has yet to be applied to a non-mammalian vertebrate. The goal of this study was to establish in vivo fast-scan cyclic voltammetry in a songbird, the European starling, to facilitate real-time measurements of extracellular catecholamine levels in the avian striatum. In urethane-anesthetized starlings, changes in catecholamine levels were evoked by electrical stimulation of the ventral tegmental area and measured at carbon–fiber microelectrodes positioned in the medial and lateral striata. Catecholamines were elicited by different stimulations, including trains related to phasic dopamine signaling in the rat, and were analyzed to quantify presynaptic mechanisms governing exocytotic release and neuronal uptake. Evoked extracellular catecholamine dynamics, maximal amplitude of the evoked catecholamine signal, and parameters for catecholamine release and uptake did not differ between striatal regions and were similar to those determined for dopamine in the rat dorsomedial striatum under similar conditions. Chemical identification of measured catecholamine by its voltammogram was consistent with the presence of both dopamine and norepinephrine in striatal tissue content. However, the high ratio of dopamine to norepinephrine in tissue content and the greater sensitivity of the carbon–fiber microelectrode to dopamine compared to norepinephrine favored the measurement of dopamine. Thus, converging evidence suggests that dopamine was the predominate analyte of the electrically evoked catecholamine signal measured in the striatum by fast-scan cyclic voltammetry. Overall, comparisons between the characteristics of these evoked signals suggested a similar presynaptic regulation of dopamine in the starling and rat striatum. Fast-scan cyclic voltammetry thus has the potential to be an invaluable tool for investigating the neural underpinnings of behavior in birds.

New Synthetic Drugs in Addictovigilance

New substances, also known as "designer drugs" or "legal highs" are increasingly available to drug users. Two hundred and fifteen hitherto unlisted substances have been notified by European Union member states since 2005. These synthetic drugs, which have been developed to side-step the legislation on drugs, are analogues or derivatives of existing drugs and medications. The availability of these "legal highs", sold on Internet under various denominations such as bath salt, plant fertilizer, chemical not intended for human use, or spice, is unlimited. The effects felt by users vary, and the substances may be stimulant, entactogenic, hallucinogenic, psychedelic or dissociative. The pharmacological targets also vary, and may be either the increase of extracellular levels of neurotransmitters via different mechanisms (reuptake inhibition, stimulation of intracellular release) or else fixation on specific receptors. Several chemical classes, themselves divided into sub-classes, are involved: phenethylamines, tryptamines, piperazines, cathinones, cannabinoids etc. The toxicity of the main members of these categories is increasingly well known, the most deleterious being behavioural effects, physical manifestations, and cardiovascular consequences. However, small variations in their chemical structure can generate effects that are quantitatively different, thus enhancing their toxicity or addictive potential, and much remains to be achieved in terms of knowledge about these new drugs. These substances are indeed present on the French territory, as shown by data provided by the Observatoire Français des Drogues et Toxicomanies, and notifications by the French Addictovigilance network. Screening in clinical toxicology laboratories is not widespread, since these molecules are not detected by the standard screening tests, so that there is probably an under-estimation of the use of these new drugs. The legislation on these substances changes regularly, with more and more countries classifying them as "narcotics" or illegal psychotropic drugs so as to restrict their use, applying a generic classification when possible.

Interpreting chemical neurotransmission in vivo: techniques, time scales, and theories.

Monitoring neurotransmitter levels is a major research strategy for determining the functions of neuronal systems, specifically the ascending neuromodulator systems. In this Viewpoint, we consider the impact of different methods for recording extracellular neurotransmitter levels in vivo on theories concerning the signaling mode(s) and functions of these neuronal systems. As exemplified by evidence from experiments using different methods to measure acetylcholine (ACh) signaling, both neuromodulatory and deterministic functions have been attributed to cholinergic activity. Technical and experimental advances now allow determination of the validity of such dual-signaling theories.

The SLC6 transporters: perspectives on structure, functions, regulation, and models for transporter dysfunction

The human SLC6 family is composed of approximately 20 structurally related symporters (co-transporters) that use the transmembrane electrochemical gradient to actively import their substrates into cells. Approximately half of the substrates of these transporters are amino acids, with others transporting biogenic amines and/or closely related compounds, such as nutrients and compatible osmolytes. In this short review, five leaders in the field discuss a number of currently important research themes that involve SLC6 transporters, highlighting the integrative role they play across a wide spectrum of different functions. The first essay, by Gary Rudnick, describes the molecular mechanism of their coupled transport which is being progressively better understood based on new crystal structures, functional studies, and modeling. Next, the question of multiple levels of transporter regulation is discussed by Reinhard Krämer, in the context of osmoregulation and stress response by the related bacterial betaine transporter BetP. The role of selected members of the human SLC6 family that function as nutrient amino acid transporters is then reviewed by François Verrey. He discusses how some of these transporters mediate the active uptake of (essential) amino acids into epithelial cells of the gut and the kidney tubule to support systemic amino acid requirements, whereas others are expressed in specific cells to support their specialized metabolism and/or growth. The most extensively studied members of the human SLC6 family are neurotransmitter reuptake transporters, many of which are important drug targets for the treatment of neuropsychiatric disorders. Randy Blakely discusses the role of posttranscriptional modifications of these proteins in regulating transporter subcellular localization and activity state. Finally, Dennis Murphy reviews how natural gene variants and mouse genetic models display consistent behavioral alterations that relate to altered extracellular neurotransmitter levels.

Vortioxetine (Lu AA21004), a novel multimodal antidepressant, enhances memory in rats

The serotonergic system plays an important role in cognitive functions via various 5-HT receptors. Vortioxetine (Lu AA21004) in development as a novel multimodal antidepressant is a 5-HT3, 5-HT7 and 5-HT1D receptor antagonist, a 5-HT1B receptor partial agonist, a 5-HT1A receptor agonist and a 5-HT transporter (5-HTT) inhibitor in vitro. Preclinical studies suggest that 5-HT3 and 5-HT7 receptor antagonism as well as 5-HT1A receptor agonism may have a positive impact on cognitive functions including memory. Thus vortioxetine may potentially enhance memory. We investigated preclinical effects of vortioxetine (1–10mg/kg administered subcutaneously [s.c.]) on memory in behavioral tests, and on cortical neurotransmitter levels considered important in rat memory function. Contextual fear conditioning and novel object recognition tests were applied to assess memory in rats. Microdialysis studies were conducted to measure extracellular neurotransmitter levels in the rat medial prefrontal cortex. Vortioxetine administered 1h before or immediately after acquisition of contextual fear conditioning led to an increase in freezing time during the retention test. This mnemonic effect was not related to changes in pain sensitivity as measured in the hotplate test. Rats treated with vortioxetine 1h before training spent more time exploring the novel object in the novel object recognition test. In microdialysis studies of the rat medial prefrontal cortex, vortioxetine increased extracellular levels of acetylcholine and histamine. In conclusion, vortioxetine enhanced contextual and episodic memory in rat behavioral models. Further demonstration of its potential effect on memory functions in clinical settings is warranted.

Antidepressant activity: contribution of brain microdialysis in knock-out mice to the understanding of BDNF/5-HT transporter/5-HT autoreceptor interactions

Why antidepressants vary in terms of efficacy is currently unclear. Despite the leadership of selective serotonin reuptake inhibitors (SSRIs) in the treatment of depression, the precise neurobiological mechanisms involved in their therapeutic action are poorly understood. A better knowledge of molecular interactions between monoaminergic system, pre- and post-synaptic partners, brain neuronal circuits and regions involved may help to overcome limitations of current treatments and identify new therapeutic targets. Intracerebral in vivo microdialysis (ICM) already provided important information about the brain mechanism of action of antidepressants first in anesthetized rats in the early 1990s, and since then in conscious wild-type or knock-out mice. The principle of ICM is based on the balance between release of neurotransmitters (e.g., monoamines) and reuptake by selective transporters [e.g., serotonin transporter for serotonin 5-hydroxytryptamine (5-HT)]. Complementary to electrophysiology, this technique reflects pre-synaptic monoamines release and intrasynaptic events corresponding to ≈80% of whole brain tissue content. The inhibitory role of serotonergic autoreceptors infers that they limit somatodendritic and nerve terminal 5-HT release. It has been proposed that activation of 5-HT1A and 5-HT1B receptor sub-types limits the antidepressant-like activity of SSRIs. This hypothesis is based partially on results obtained in ICM experiments performed in naïve, non-stressed rodents. The present review will first remind the principle and methodology of ICM performed in mice. The crucial need of developing animal models that display anxiety and depression-like behaviors, neurochemical and brain morphological phenotypes reminiscent of these mood disorders in humans, will be underlined. Recently developed genetic mouse models have been generated to independently manipulate 5-HT1A auto and heteroreceptors and ICM helped to clarify the role of the pre-synaptic component, i.e., by measuring extracellular levels of neurotransmitters in serotonergic nerve terminal regions and raphe nuclei. Finally, we will summarize main advantages of using ICM in mice through recent examples obtained in knock-outs (drug infusion through the ICM probe allows the search of a correlation between changes in extracellular neurotransmitter levels and antidepressant-like activity) or alternatives (infusion of a small-interfering RNA suppressing receptor functions in the mouse brain). We will also focus this review on post-synaptic components such as brain-derived neurotrophic factor in adult hippocampus that plays a crucial role in the neurogenic and anxiolytic/antidepressant-like activity of chronic SSRI treatment. Limitations of ICM will also be considered.

Astrocytic regulation of glutamate homeostasis in epilepsy.

Astrocytes play a critical role in regulation of extracellular neurotransmitter levels in the central nervous system. This function is particularly prominent for the excitatory amino acid glutamate, with estimates that 80-90% of extracellular glutamate uptake in brain is through astrocytic glutamate transporters. This uptake has significance both in regulation of the potential toxic accumulation of extracellular glutamate and in normal resupply of inhibitory and excitatory synapses with neurotransmitter. This resupply of neurotransmitter is accomplished by astroglial uptake of glutamate, transformation of glutamate to glutamine by the astrocytic enzyme glutamine synthetase (GS), and shuttling of glutamine back to excitatory and inhibitory neurons via specialized transporters. Once in neurons, glutamine is enzymatically converted back to glutamate, which is utilized for synaptic transmission, either directly, or following decarboxylation to γ-aminobutyric acid. Many neurologic and psychiatric conditions, particularly epilepsy, are accompanied by the development of reactive gliosis, a pathology characterized by anatomical and biochemical plasticity in astrocytes, accompanied by proliferation of these cells. Among the biochemical changes evident in reactive astrocytes is a downregulation of several of the important regulators of the glutamine-glutamate cycle, including GS, and possibly also glutamate transporters. This downregulation may have significance in contributing both to the aberrant excitability and to the altered neuropathology characterizing epilepsy. In the present review, we provide an overview of the normal function of astrocytes in regulating extracellular glutamate homeostasis, neurotransmitter supply, and excitotoxicity. We further discuss the potential role reactive gliosis may play in the pathophysiology of epilepsy.

Lobeline Attenuates the Locomotor-Activating Properties of Repeated Morphine Treatment in Rats

Purpose: Lobeline perturbs intra- and extracellular neurotransmitter levels and diminishes the in vitro and in vivo effects of psychostimulants. More recently, lobeline was shown to bind to μ opiate receptors, block the effects of opiate receptor agonists, and decrease heroin self-administration in rats. The present study determined the effect of lobeline on morphine-induced changes in locomotor behavior in rats. Methods: For 12 consecutive days (Days 1 - 12), male rats were administered lobeline (0.3 or 1 mg/kg) followed by morphine (5 or 10 mg/kg) and locomotor activity was measured. On Day 13, the effect of lobeline on the expression of morphine-induced increases in activity was determined. Results: With repeated morphine treatment, an increase in locomotor activity was observed. In a dosedependent manner, lobeline decreased the morphine-induced increase in activity. Acute lobeline challenge on Day 13 also attenuated the expression of this morphine-induced increase in activity. Conclusion: These results are consistent with previous work where lobeline blocks the locomotoractivtating properties of psychostimulants, and these findings support an emerging literature suggesting that lobeline produces its behavioral effects through an interaction with μ opiate receptors. Keywords: Behavior, Morphine, Locomotor activity, Behavioural sensitization, μ Opiate receptors

Simultaneous quantitation of histamine and its major metabolite 1-methylhistamine in brain dialysates by using precolumn derivatization prior to HILIC-MS/MS analysis

In nonclinical drug development targeting the central nervous system (CNS), the quantitative determination of extracellular brain concentrations of neurotransmitters is a key challenge. In some CNS disorders, the monitoring of the modified profile of neurotransmitter release such as that of histamine may explain the mechanism of action of the drug candidate. Microdialysis is a commonly used method for sampling extracellular levels of neurotransmitters/drug candidates in small laboratory animals. Detection and quantification of extracellular levels of neurotransmitters remain an analytical and technical challenge owing to the low concentrations of neurotransmitters collected, the small microdialysis sample size, and the high amount of inorganic salts. A precolumn derivatization strategy prior to hydrophilic interaction liquid chromatography (HILIC)-tandem mass spectrometry analysis is proposed to quantify histamine release after administration of a CNS research compound. Derivatization using propionic anhydride dissolved in organic solvent combined with the HILIC approach effectively eliminated three time-consuming steps, organic layer transfer, dry down, and reconstitution, all of which are required by traditional reversed-phase liquid chromatography. The formation of propionylated amides, performed under mild conditions, required no further sample cleanup. After a dual microdialysis probe implantation into the prefrontal cortex (neurotransmitters) and in the inferior vena cava of rat (drug candidate), microdialysate fractions were collected every 15 min for 8 h and stored frozen at -20 °C until analysis. The method was validated using 10 μL microdialysate, achieving low limits of quantitation of 83.4 and 84.5 pg.mL(-1) for histamine and 1-methylhistamine, respectively. These limits were suitable to assess kinetic release of neurotransmitters and are compatible with those obtained by microdialysis sampling. This method provided the required selectivity, sensitivity, accuracy, and precision to assess release kinetics of histamine and 1-methylhistamine in several hundred rat brain microdialysates after intravenous infusion of CNS drug candidates.

Effects of methylphenidate: the cellular point of view

The psychostimulant methylphenidate (MPH) is the first choice of treatment in attention-deficit hyperactivity disorder and is based mainly on inhibition of dopamine transporter (DAT). Nonetheless, the complete cellular effects of MPH are still unknown. We attempted to determine whether MPH influences neurotransmitter levels, synaptic gene expression, and cell proliferation in a dose-dependent manner in rat pheochromocytoma cells (PC12) lacking DAT. PC12 were treated in a dose-dependent manner with MPH. Gene expression level of synaptotagmin (Syt) 1 and 4, syntaxin 1a (Stx1a), and synaptic vesicle glycoprotein 2C (SV2C) was measured using quantitative real-time RT-PCR. Different Neurotransmitter release was measured using high-performance liquid chromatography (HPLC). Differences in cell proliferation were evaluated via BrdU incorporation. Treatment with low-dose MPH (1-100 nM) altered intra-/extracellular neurotransmitter levels, down-regulated all investigated genes as well as enhanced cell proliferation significantly. These data point to diverse effects of MPH on cell metabolism independent of inhibiting DAT.

ORIGINAL RESEARCH—BASIC SCIENCE: Acute and Repeated Flibanserin Administration in Female Rats Modulates Monoamines Differentially Across Brain Areas: A Microdialysis Study

Hypoactive sexual desire disorder (HSDD) is defined as persistent lack of sexual fantasies or desire marked by distress. With a prevalence of 10% it is the most common form of female sexual dysfunction. Recently, the serotonin-1A (5-HT(1A)) receptor agonist and the serotonin-2A (5-HT(2A)) receptor antagonist flibanserin were shown to be safe and efficacious in premenopausal women suffering from HSDD in phase III clinical trials. The current study aims to assess the effect of flibanserin on neurotransmitters serotonin (5-HT), norepinephrine (NE), dopamine (DA), glutamate, and gamma-aminobutyric acid (GABA) in brain areas associated with sexual behavior. Flibanserin was administered to female Wistar rats (280-350 g). Microdialysis probes were stereotactically inserted into the mPFC, NAC, or MPOA, under isoflurane anesthesia. The extracellular levels of neurotransmitters were assessed in freely moving animals, 24 hours after the surgery. Dialysate levels of DA, NE, and serotonin from medial prefrontal cortex (mPFC), nucleus accumbens (NAC), and hypothalamic medial preoptic area (MPOA) from female rats. Acute flibanserin administration decreased 5-HT and increased NE levels in all tested areas. DA was increased in mPFC and MPOA, but not in the NAC. Basal levels of NE in mPFC and NAC and of DA in mPFC were increased upon repeated flibanserin administration, when compared to vehicle-treated animals. The basal levels of 5-HT were not altered by repeated flibanserin administration, but basal DA and NE levels were increased in the mPFC. Glutamate and GABA levels remained unchanged following either repeated or acute flibanserin treatment. Systemic administration of flibanserin to female rats differentially affects the monoamine systems of the brain. This may be the mechanistic underpinning of flibanserin's therapeutic efficacy in HSDD, as sexual behavior is controlled by an intricate interplay between stimulatory (catecholaminergic) and inhibitory (serotonergic) systems.

Intracerebral microdialysis during deep brain stimulation surgery

BackgroundThis report describes the use of microdialysis in conjunction with deep brain stimulation (DBS) surgery to assess extracellular levels of neurotransmitters within the human basal ganglia (BG). Electrical stimulation of the subthalamic nucleus (STN) is an efficacious treatment for advanced Parkinson's disease, yet the mechanisms of STN DBS remain poorly understood. Measurement of neurotransmitter levels within the BG may provide insight into mechanisms of DBS, but such an approach presents technical challenges. MethodsAfter microelectrode recordings confirmed location of STN, a custom microdialysis guide cannula was inserted. A CMA (Stockholm, Sweden) microdialysis probe was then positioned to the same depth as the microrecording electrode in STN or 2mm inferiorly to record in the substantia nigra. The catheter was perfused at a rate of 2.0μL/min with a sterile mock CSF solution and samples of extracellular fluid were collected at regular intervals. Dialysate samples were analyzed using high-pressure liquid chromatography (HPLC) detection procedures for quantitation of glutamate, gamma-aminobutyric acid (GABA), and dopamine. ResultsLevels of neurotransmitters were reliably identified in dialysate samples using HPLC. By monitoring concentrations of glutamate, GABA and dopamine, we were able to demonstrate what seemed to be a steady state baseline within approximately 30min. ConclusionMicrodialysis during DBS surgery is a feasible method for assessing levels of glutamate, GABA and dopamine within the human BG. Obtaining a steady state baseline of neurotransmitter levels appears feasible, thus making future studies of intraoperative microdialysis during DBS meaningful.

Simultaneous monitoring multiple neurotransmitters and neuromodulators during cerebral ischemia/reperfusion in rats by microdialysis and capillary electrophoresis

In this work, focal cerebral ischemia/reperfusion was induced by the model of middle cerebral artery occlusion. The dialysates of extracellular fluid in hypothalamus were obtained by using brain microdialysis technique. An efficient and sensitive chiral capillary electrophoresis with laser-induced fluorescence detection procedure was developed for the simultaneous determination of multiple amino acids neurotransmitter including Arg, Lys, Trp, GABA, l-Ser, Ala, Tau, Gly, Glu and Asp; catcholamine (dopamine) and neuromodulator ( d-Ser and O-phosphoethanolamine) in microdialysate. Different parameters that influenced CE separation were optimized. The optimal method was used to investigate the dynamic changes of neurotransmitters and neuromodulators during cerebral ischemia/reperfusion. The results indicated that extracellular levels of multiple neurotransmitters and neuromodulators were elevated during cerebral ischemia/reperfusion. The dynamic changes and functional status of releasable neurotransmitters and neuromodulators during ischemia/reperfusion were discussed.

Evaluation of metaquant microdialysis for measurement of absolute concentrations of amphetamine and dopamine in brain: A viable method for assessing pharmacokinetic profile of drugs in the brain

Direct measurement of absolute brain concentration of amphetamine and dopamine were obtained using metaquant (MQ) microdialysis, which achieves near 100% recovery, in the caudate nucleus. Conventional microdialysis monoprobes were also implanted in the caudate nucleus in the contralateral side of the same animals to compare the brain concentrations obtained from these two probe types. In addition plasma concentrations of amphetamine were obtained simultaneously from the same animals. The distribution of amphetamine in the plasma and of amphetamine and dopamine in both probe types followed same profile at each time interval. The basal dialysate concentration of dopamine in the caudate nucleus measured by MQ, was 9.40±0.60nM, while measured by conventional microdialysis it was 6.35±0.36nM. This study demonstrates that MQ microdialysis is an appropriate method for determination of true extracellular levels of drugs and neurotransmitters in the brain, under dynamic conditions. Since these measurements, together with measurements of plasma concentrations of the drug, can be made in a single animal, the method can be used to study pharmacokinetic–pharmacodyamics profile of psychoactive agents.

Effect of sertindole on extracellular dopamine, acetylcholine, and glutamate in the medial prefrontal cortex of conscious rats: a comparison with risperidone and exploration of mechanisms involved

Second-generation antipsychotics have some beneficial effect on cognition. Recent studies, furthermore, indicate differential effects of second-generation antipsychotics on impairment in executive cognitive function. We evaluated the effect of the second-generation antipsychotic drug, sertindole, on extracellular levels of dopamine (DA), acetylcholine (ACh), and glutamate (Glu) in the rat medial prefrontal cortex (mPFC). Risperidone was studied for comparison. Moreover, selective serotonin 5-HT(2A), 5-HT(2C), and 5-HT(6) receptor antagonists were used, given alone and in combination with the preferential DA D(2) receptor antagonist, haloperidol, to further clarify the action of the two drugs. Rats were treated acutely with vehicle or drugs, and extracellular levels of neurotransmitters were assessed by microdialysis in freely moving animals. Sertindole and risperidone significantly increased extracellular levels of DA. Haloperidol; the 5-HT(2A) receptor antagonist, M100907; the 5-HT(2C) receptor antagonist, SB242084; and the 5-HT(6) receptor antagonist, GSK-742457, induced minor increases in levels of DA, but the three latter compounds raised the DA levels notably in combination with haloperidol. Sertindole and risperidone significantly increased the extracellular levels of ACh but only sertindole raised the extracellular levels of Glu. The selective 5-HT(6) receptor antagonist, SB-271046, significantly increased the extracellular levels of Glu. Sertindole and risperidone markedly increased extracellular levels of DA in mPFC. The built-in 5-HT(2A)/5-HT(2C)/D(2) receptor antagonism of the two drugs might be involved in this action. Both drugs increased the extracellular levels of ACh but only sertindole enhanced Glu levels. The high affinity of sertindole for the 5-HT(6) receptor compared to risperidone may differentiate sertindole from risperidone.

Effects of zotepine on extracellular levels of monoamine, GABA and glutamate in rat prefrontal cortex

The atypical antipsychotic drug, zotepine, is effective in treatment of schizophrenia and acute mania, but the incidence of seizures during treatment is higher than with other antipsychotics. In addition, the mechanisms underlying the clinical actions of zotepine remain uncharacterized. The effects of intraperitoneal administration of zotepine and haloperidol on the extracellular levels of noradrenaline, dopamine, 5-HT, GABA, and glutamate in the medial prefrontal cortex (mPFC) were compared. Neuronal activities induced by each drug in the ventral tegmental area (VTA), locus coeruleus (LC), dorsal raphe nucleus (DRN) and mediodorsal thalamic nucleus (MTN) were also analysed. Haloperidol did not affect extracellular neurotransmitter levels in the mPFC. In contrast, zotepine activated neuronal activities in all nuclei and increased the extracellular levels of noradrenaline, dopamine, GABA, and glutamate in the mPFC, but not 5-HT levels. The zotepine-stimulated neuronal activity in the VTA, LC, DRN and MTN enhanced the release of dopamine, noradrenaline, 5-HT, glutamate and GABA in the mPFC, although the enhanced GABAergic transmission possibly inhibited noradrenaline, dopamine and 5-HT release. The other afferent to mPFC, which releases dopamine and noradrenaline, was partially insensitive to GABAergic inhibition, but possibly received stimulatory AMPA/glutamatergic regulation from the MTN. Our results indicated that the positive interaction between prefrontal catecholaminergic transmission and AMPA/glutamatergic transmission from MTN might explain the regulatory effects of zotepine on neurotransmitter release. A mechanism is suggested to account for the pharmacological profile of this atypical antipsychotic and for its pro-convulsive action.

Zonisamide enhances delta receptor-associated neurotransmitter release in striato-pallidal pathway

A recent randomized control study demonstrated that zonisamide (ZNS), an antiepileptic drug, is effective in Parkinson's disease at the lower than the therapeutic doses against epilepsy (25–50 mg/day); however, the detailed mechanism of antiparkinsonian effects of ZNS remains to be clarified. To determine the mechanism of antiparkinsonian effect of ZNS, we investigated the effects of ZNS on extracellular levels of dopamine in the striatum (STR), glutamate in substantia nigra pars reticulata (SNr), GABA in globus pallidus (GP), subthalamic nucleus (STN) and SNr, using multiple microdialysis probes. Striatal perfusion of 1000 μM ZNS (within therapeutic-relevant concentration against epilepsy) increased extracellular levels of dopamine in STR, whereas 100 μM ZNS (lower than the therapeutic-relevant concentration against epilepsy but within the therapeutic rage against Parkinson's disease) did not affect it. Striatal perfusion of ZNS (100 and 1000 μM) decreased the extracellular levels of GABA in STN and glutamate in SNr, but decreased extracellular GABA level in GP without affecting GABA level in SNr. These concentration-dependent effects of ZNS on extracellular neurotransmitter levels were independent of dopamine and δ 2 receptors; however, blockade of δ 1 receptor inhibited the effects of ZNS. Furthermore, activation of δ 1 receptor enhanced the effects of ZNS on neurotransmitter level. These results suggest that ZNS does not affect the direct pathway but inhibits the indirect pathway, which is mediated by δ 1 receptor. Therefore, the antiparkinsonian effects of ZNS seem to be mediated through the interaction between lower than therapeutically-relevant concentration against epilepsy of ZNS (100 μM) and δ 1 receptor.

Degeneration of Astrocytic Processes and Their Mitochondria in Cerebral Cortical Regions Peripheral to the Cortical Infarction

Astrocytes support neuronal functions by regulating the extracellular ion-homeostasis and levels of neurotransmitters, and by providing fuel such as lactate to the neurons via their astrocytic processes (APs). Whether injured APs are associated with neuronal survival/death is still an unanswered question. We investigated APs in the neuropil, especially those around astrocytes and normal-appearing, degenerating, and dead neurons in cerebral cortical regions peripheral to the cortical infarction (RPI). Stroke-positive gerbils were euthanized at various times after the ischemic insult. Ultrathin sections were obtained from the RPI sectioned coronally at the infundibular level. We counted the number of normal-appearing, degenerated, and dead neurons and astrocytes in paraffin sections, the number of cut-ends and mitochondria in APs in the neuropil on electron-microscopic photographs, and determined the percent-volume of APs by Weibel point-counting method. We compared the number of cut-ends and mitochondria and percent-volume of APs around astrocytes at 5 hours and 48 hours, and around normal-appearing, degenerated, and dead neurons at 12 hours. Although the number of astrocytes did not change (average of 12.3+/-0.20%) during 0 to 48 hours, that of the dead neurons increased from 9.71+/-1.34 to 44.39+/-1.40% during 5 to 48 hours postischemia. The number of normal-appearing APs and mitochondria in APs decreased respectively from 13.49+/-0.65 to 1.61+/-0.14/28.20 microm(2) and from 1.86+/-0.18 to 0.61+/-0.07/28.20 microm(2) in the neuropil during 0 to 48 hours. The number of normal-appearing APs around astrocytes decreased from 12.3+/-0.19 to 1.7+/-0.05/38.33 microm(2) with an increase in percent-volume of degenerated APs from 1.17+/-0.04 to 11.45+/-0.23%, from 5 to 48 hours postischemia. The number of normal-appearing APs decreased from 4.36+/-0.52 to 1.56+/-0.17/38.33 microm(2) with an increase in percent-volume of degenerated APs, from 2.41+/-0.52 to 12.55+/-1.0%, from around the normal-appearing to dead neurons, at 12 hours. In the RPI, heterogeneous degeneration of APs was closely associated with disseminated selective neuronal necrosis and the maturation phenomenon seen in ischemic neuronal injury.

Taste reward modulates neuronal responses to preceding visual stimuli in the rat V2 neocortex

Event Abstract Back to Event Taste reward modulates neuronal responses to preceding visual stimuli in the rat V2 neocortex Istvan Hernadi1*, Norbert Burkus1, Gergely Orsi1, Anita Kovacs1 and Lorand Kellenyi1 1 Department of Experimental Zoology and Neurobiology, Institute of Biology, University of Pecs, Hungary With a newly developed technique, a universal biopotentiostat and biological amplifier were combined for neurophysiological and electroanalytical measurement purposes to detect rapid changes in extracellular neurotransmitter levels, whilst recording in vivo single unit activity of the target neurons. Using carbon-fibre multibarrel electrodes, and microiontophoresis pumps in the same experiment, enabled neurochemical identification of the target cells. To test the validity of the above technique under in vivo conditions, we recorded neuronal activity (n=185) in the visual neocortex (V2ML) of 38 anesthetized wistar rats. During recording, we performed standard Pavlovian reward conditioning, using two types of light flashes (high power LEDs) as conditioning stimuli (CS+) or yoked randomised light flashes (CS-) as control stimuli. In each trial, the CS+ was present for 1000ms, followed by 500ms delay. We applied ~0,35ml 0,5M sucrose solution as unconditioned stimulus (US). At the end of each trial, distilled water was applied to the mouth. Twenty-five per cent of all neurons showed response to CS+ or CS- outside the context. Among light responsive neurons, a majority of 34 % developed a context-dependent (CS-US) response, consequently taking part in the rapid, light-associated learning procedure. Light responses of neurons changed only to previously paired stimulus (CS+), but remained constant to the yoked light stimulus (CS-). We successfully used the combination of neurophysiological and electrochemical techniques to describe rapid stimulus-reinforcement learning in the rat V2 under in vivo conditions. Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Research on the cerebral cortex and related structures Citation: Hernadi I, Burkus N, Orsi G, Kovacs A and Kellenyi L (2009). Taste reward modulates neuronal responses to preceding visual stimuli in the rat V2 neocortex. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.196 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 06 Mar 2009; Published Online: 06 Mar 2009. * Correspondence: Istvan Hernadi, Department of Experimental Zoology and Neurobiology, Institute of Biology, University of Pecs, Pecs, Hungary, hernadi@gamma.ttk.pte.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Istvan Hernadi Norbert Burkus Gergely Orsi Anita Kovacs Lorand Kellenyi Google Istvan Hernadi Norbert Burkus Gergely Orsi Anita Kovacs Lorand Kellenyi Google Scholar Istvan Hernadi Norbert Burkus Gergely Orsi Anita Kovacs Lorand Kellenyi PubMed Istvan Hernadi Norbert Burkus Gergely Orsi Anita Kovacs Lorand Kellenyi Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Survivable Stereotaxic Surgery in Rodents

The ability to measure extracellular basal levels of neurotransmitters in the brain of awake animals allows for the determination of effects of different systemic challenges (pharmacological or physiological) to the CNS. For example, one can directly measure how the animal's midbrain dopamine projections respond to dopamine-releasing drugs like d-amphetamine or natural stimuli like food. In this video, we show you how to implant guide cannulas targeting specific sites in the rat brain, how to insert and implant a microdialysis probe and how to use high performance liquid chromatography coupled with electrochemical detection (HPLC-EC) to measure extracellular levels of oxidizable neurotransmitters and metabolites. Local precise introduction of drugs through the microdialysis probe allows for refined work on site specificity in a compound s mechanism of action. This technique has excellent anatomical and chemical resolution but only modest time resolution as microdialysis samples are usually processed every 20-30 minutes to ensure detectable neurotransmitter levels. Complementary ex vivo tools (i.e., slice and cell culture electrophysiology) can assist with monitoring real-time neurotransmission.