Reverse Microdialysis Research Articles

Gastrin response to candidate messengers in intact conscious rats monitored by antrum microdialysis

We monitored gastrin release in response to locally applied candidate messengers in intact conscious rats. Earlier studies have been performed on anaesthetized animals, isolated pieces of antrum, or purified preparations of gastrin cells. In this study we created an experimental situation to resemble physiological conditions, using reverse microdialysis to administer regulatory peptides and amines that might affect gastrin secretion. Microdialysis probes were implanted in the submucosa of the antrum of the rat stomach. Three days later, putative messenger compounds were administered via the probe. Their effects on basal (24 h fast) and omeprazole-stimulated (400 μmol/kg/day, 4 days peroral administration) gastrin release were monitored by continuous measurement (3 h) of gastrin in the perfusate (radioimmunoassay). Fasted rats (low microdialysate gastrin, 2.1 ± 0.1 pmol l − 1 ) were used to study stimulation of gastrin release. Omeprazole-treated rats (high microdialysate gastrin, 95.8 ± 6.7 pmol l − 1 ) were used to study suppression of gastrin release. The following agents raised the concentration of microdialysate gastrin (peak response): gastrin-releasing peptide (GRP) (11-fold increase at a near-maximal dose), carbachol (5-fold increase), serotonin (2-fold increase) and isoprenaline (20-fold increase). Adrenaline and noradrenaline induced transient but powerful elevation (40- and 20-fold increase). Somatostatin, galanin and bradykinin (at near-maximal doses) suppressed omeprazole-stimulated gastrin release (50% decrease). Calcitonin gene-related peptide, ghrelin, gastric inhibitory peptide, motilin, neurotensin, neuromedin U-25, peptide YY and vasoactive intestinal peptide were without effect on gastrin release, as were aspartate, γ-aminobutyric acid, glutamate, glycine, dopamine and histamine. The results support the view that G cells operate under neurocrine/paracrine control. They were stimulated by agents present in enteric neurons (GRP, galanin, choline ester and catechol amines) and in gastric endocrine cells (serotonin). They were inhibited by somatostatin (D cell peptide), galanin (neuropeptide) and by the inflammatory agent bradykinin.

GABAergic regulation of the perifornical–lateral hypothalamic neurons during non-rapid eye movement sleep in rats

The perifornical–lateral hypothalamic area (PF–LHA) has been implicated in the regulation of behavioral arousal. The PF–LHA predominantly contains neurons that are active during behavioral and cortical activation and quiescent during non-rapid eye movement (nonREM) sleep, that is, are nonREM-off neurons. Some in vitro and in vivo studies indicate that PF–LHA neurons, including hypocretin-expressing neurons, are under GABAergic control. However, a role of GABA in suppressing the discharge of PF–LHA neurons during spontaneous nonREM sleep has not been confirmed. We recorded the sleep–wake discharge profiles of PF–LHA neurons and simultaneously assessed the contributions of local GABA A receptor activation and blockade on their wake- and nonREM sleep-related discharge activities by delivering GABA A receptor agonist, muscimol (500 nm, 5 μM, and 10 μM) and its antagonist, bicuculline (5 μM, 10 μM, and 20 μM), adjacent to the recorded neurons via reverse microdialysis. Muscimol dose-dependently decreased the discharge of PF–LHA neurons including nonREM-off neurons. Muscimol-induced suppression of discharge during nonREM sleep was significantly weaker than the suppression produced during waking. In the presence of bicuculline, PF–LHA neurons, including nonREM-off neurons, exhibited elevated discharge, which was dose-dependent and was significantly higher during nonREM sleep, compared to waking. These results suggest that GABA A receptor mediated increased GABAergic tone contributes to the suppression of PF–LHA neurons, including nonREM-off neurons, during spontaneous nonREM sleep.

In vivo investigation of brain and systemic ketobemidonemetabolism

Ketobemidone metabolites have previously been identified in urine and plasma; here we show, for the first time, that norketobemidone and ketobemidone N-oxide are present in in vivo microdialysate from rat brain (striatum) after reverse microdialysis, suggesting striatal metabolism of ketobemidone. Ketobemidone metabolites were also identified in in vivo microdialysate samples from brain and blood, as well as in urine from rats, after subcutaneous administration of ketobemidone. Three Phase I metabolites (norketobemidone, ketobemidone N-oxide and hydroxymethoxyketobemidone) and three Phase II metabolites (glucuronic acid conjugates of ketobemidone, norketobemidone and hydroxymethoxyketobemidone) were identified in the microdialysates after subcutaneous administration. Coupled capillary liquid chromatography tandem mass spectrometry (LC-MS/MS) and SPE (boronate)-MS/MS were utilized for the analysis of the biological samples. The Phase I metabolites were identified by comparing the retention times and tandem mass spectra of the microdialysates with synthetic standards. The Phase II metabolites were identified by determination of exact masses and by comparing the tandem mass spectra of the microdialysates with those of synthetic standards for the aglycones. Hydroxyketobemidone, a catechol-type Phase I metabolite, was selectively isolated by solid-phase boronate-complexation but identified in urine alone. This work demonstrated that the in vivo microdialysis technique in combination with LC-MS/MS can be used to study the local metabolism of a drug in the brain.

A longitudinal study of 5-HT outflow during chronic fluoxetine treatment using a new technique of chronic microdialysis in a highly emotional mouse strain

The onset of a therapeutic response to antidepressant treatment exhibits a delay of several weeks. The present study was designed to know whether extracellular serotonin (5-HT) levels need to be increased in territories of 5-HT innervation in order to obtain beneficial effects from a chronic treatment with a serotonin-selective reuptake inhibitor (SSRI). Thus, we performed a longitudinal study of a chronic fluoxetine treatment in a model of highly emotional mice (BALB/cJ). The function of the 5-HT system in the raphe nuclei and hippocampus, was assessed by using repeated in vivo microdialysis sessions in awake freely moving mice, then studying its relation with behavior, analyzed mainly with open field paradigm. One of the neural mechanisms underlying such delay has been proposed to be the functional status of 5-HT1A autoreceptors in raphe nuclei. Thus, we also assessed the degree of 5-HT1A autoreceptor desensitization by using a local infusion in the raphe of the antagonist, WAY 100635 via reverse microdialysis. We report that the anxiolytic-like effects of fluoxetine correlate in time and amplitude with 5-HT1A autoreceptor desensitization, but neither with the extracellular levels of 5-HT in the raphe nuclei, nor in the hippocampus. Our study suggests that the beneficial anxiolytic/antidepressant-like effects of chronic SSRI treatment indeed depend on 5-HT1A autoreceptor internalization, but do not require a sustained increase in extracellular 5-HT levels in a territory of 5-HT projection such as hippocampus.

Regulation of striatal nitric oxide synthesis by local dopamine and glutamate interactions

Nitric oxide (NO) is a key neuromodulator of corticostriatal synaptic transmission. We have shown previously that dopamine (DA) D1/5 receptor stimulation facilitates neuronal NO synthase (nNOS) activity in the intact striatum. To study the impact of local manipulations of D1/5 and glutamatergic NMDA receptors on striatal nNOS activity, we combined the techniques of in vivo amperometry and reverse microdialysis. Striatal NO efflux was monitored proximal to the microdialysis probe in urethane-anesthetized rats during local infusion of vehicle or drug. NO efflux elicited by systemic administration of SKF-81297 was blocked following intrastriatal infusion of: (i) the D1/5 receptor antagonist SCH-23390, (ii) the nNOS inhibitor 7-nitroindazole, (iii) the non-specific ionotropic glutamate receptor antagonist kynurenic acid, and (iv) the selective NMDA receptor antagonist 3-phosphonopropyl-piperazine-2-carboxylic acid. Glycine co-perfusion did not affect SKF-81297-induced NO efflux. Furthermore, intrastriatal infusion of SKF-81297 potentiated NO efflux evoked during electrical stimulation of the motor cortex. The facilitatory effects of cortical stimulation and SKF-81297 were both blocked by intrastriatal infusion of SCH-23390, indicating that striatal D1/5 receptor activation is necessary for the activation of nNOS by corticostriatal afferents. These studies demonstrate for the first time that reciprocal DA-glutamate interactions play a critical role in stimulating striatal nNOS activity.

A single, moderate ethanol exposure alters extracellular dopamine levels and dopamine d receptor function in the nucleus accumbens of wistar rats.

The nucleus accumbens (NAc) has been implicated in the neurochemical effects of ethanol (EtOH). Evidence suggests that repeated EtOH exposures and chronic EtOH drinking increase dopamine (DA) neurotransmission in the NAc due, in part, to a reduction in D(2) autoreceptor function. The objectives of the current study were to evaluate the effects of a single EtOH pretreatment and repeated EtOH pretreatments on DA neurotransmission and D(2) autoreceptor function in the NAc of Wistar rats. Experiment 1 examined D(2) receptor function after a single intraperitoneal (i.p.) injection or repeated i.p. injections of 0.0, 0.5, 1.0, or 2.0 g/kg EtOH to female Wistar rats. Single EtOH pretreatment groups received 1 daily i.p. injection of 0.9% NaCl (saline) for 4 days, followed by 1 day of saline or EtOH administration; repeated EtOH pretreatment groups received 5 days of saline or EtOH injections. Reverse microdialysis experiments were conducted to determine the effects of local perfusion with the D(2)-like receptor antagonist (-)sulpiride (SUL; 100 uM), on extracellular DA levels in the NAc. Experiment 2 evaluated if pretreatment with a single, moderate (1.0 g/kg) dose of EtOH would alter levels and clearance of extracellular DA in the NAc, as measured by no-net-flux (NNF) microdialysis. Subjects were divided into the EtOH-naïve and the single EtOH pretreated groups from Experiment 1. Experiment 1: Changes in extracellular DA levels induced with SUL perfusion were altered by the EtOH dose (p < 0.001), but not the number of EtOH pretreatments (p > 0.05). Post-hoc analyses indicated that groups pretreated with single or repeated 1.0 g/kg EtOH showed significantly attenuated DA response to SUL, compared with all other groups (p < 0.001). Experiment 2: Multiple linear regression analyses yielded significantly (p < 0.05) higher extracellular DA concentrations in the NAc of rats receiving EtOH pretreatment, compared with their EtOH-naïve counterparts (3.96 +/- 0.42 nM and 3.25 +/- 0.23 nM, respectively). Extraction fractions were not significantly different between the 2 groups. The present results indicate that a single EtOH pretreatment at a moderate dose can increase DA neurotransmission in the NAc due, in part, to reduced D(2) autoreceptor function.

Role of adenosine A 1 receptor in the perifornical–lateral hypothalamic area in sleep–wake regulation in rats

The perifornical–lateral hypothalamic area (PF-LHA) has been implicated in the regulation of arousal. The PF-LHA contains wake-active neurons that are quiescent during non-REM sleep and in the case of neurons expressing the peptide hypocretin (HCRT), quiescent during both non-REM and REM sleep. Adenosine is an endogenous sleep factor and recent evidence suggests that adenosine via A 1 receptors may act on PF-LHA neurons to promote sleep. We examined the effects of bilateral activation as well as blockade of A 1 receptors in the PF-LHA on sleep–wakefulness in freely behaving rats. The sleep–wake profiles of male Wistar rats were recorded during reverse microdialysis perfusion of artificial cerebrospinal fluid (aCSF) and two doses of adenosine A 1 receptor antagonist, 1,3-dipropyl-8-phenylxanthine (CPDX; 5 μM and 50 μM) or A 1 receptor agonist, N 6-cyclopentyladenosine (CPA; 5 μM and 50 μM) into the PF-LHA for 2 h followed by 4 h of aCSF perfusion. CPDX perfused into the PF-LHA during lights-on phase produced arousal ( F = 7.035, p < 0.001) and concomitantly decreased both non-REM ( F = 7.295, p < 0.001) and REM sleep ( F = 3.456, p < 0.004). In contrast, CPA perfused into the PF-LHA during lights-off phase significantly suppressed arousal ( F = 7.891, p < 0.001) and increased non-REM ( F = 8.18, p <0.001) and REM sleep ( F = 30.036, p < 0.001). These results suggest that PF-LHA is one of the sites where adenosine, acting via A 1 receptors, inhibits PF-LHA neurons to promote sleep.

Differential effects of γ‐secretase and BACE1 inhibition on brain Aβ levels in vitro and in vivo

Alzheimer's disease (AD) is hypothesized to result from elevated brain levels of beta-amyloid peptide (Abeta) which is the main component of plaques found in AD brains and which cause memory impairment in mice. Therefore, there has been a major focus on the development of inhibitors of the Abeta producing enzymes gamma-secretase and beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1). In this study, we investigated the Abeta-lowering effects of the BACE1 inhibitor LY2434074 in vitro and in vivo, comparing it to the well characterized gamma-secretase inhibitor LY450139. We sampled interstitial fluid Abeta from awake APPswe/PS1dE9 AD mice by in vivo Abeta microdialysis. In addition, we measured levels of endogenous brain Abeta extracted from wildtype C57BL/6 mice. In our in vitro assays both compounds showed similar Abeta-lowering effects. However, while systemic administration of LY450139 resulted in transient reduction of Abeta in both in vivo models, we were unable to show any Abeta-lowering effect by systemic administration of the BACE1 inhibitor LY2434074 despite brain exposure exceeding the in vitro IC(50) value several fold. In contrast, significant reduction of 40-50% of interstitial fluid Abeta and wildtype cortical Abeta was observed when infusing LY2434074 directly into the brain by means of reverse microdialysis or by dosing the BACE1 inhibitor to p-glycoprotein (p-gp) mutant mice. The effects seen in p-gp mutant mice and subsequent data from our cell-based p-gp transport assay suggested that LY2434074 is a p-gp substrate. This may partly explain why BACE1 inhibition by LY2434074 has lower in vivo efficacy, with respect to decreased Abeta40 levels, compared with gamma-secretase inhibition by LY450139.

Control of within-binge cocaine-seeking by dopamine and glutamate in the core of nucleus accumbens

Dopamine and glutamate are thought to interact in the ventral striatum and to play important roles there in the cocaine-seeking of cocaine-experienced animals. We sought to determine the relative roles of the two transmitters in the two major zones of the nucleus accumbens (NAS), the core and shell subregions. We assessed the effects of dopamine and glutamate receptor blockade in the core and shell on intravenous cocaine self-administration in rats. Trained animals were allowed to self-administer cocaine for an initial hour, and then D1-type or D2-type dopamine receptor blockers or NMDA-type or AMPA-type glutamate receptor blockers were infused by reverse microdialysis into one of the two regions for an additional 3 h of testing. The D1-type antagonist SCH23390 and the D2-type antagonist raclopride each increased cocaine intake whereas the AMPA-type antagonist CNQX decreased responding when infused into the core. SCH23390 increased cocaine intake less strongly when infused into the shell, while raclopride and CNQX were each ineffective when infused into the shell. The NMDA-antagonist CPP failed to affect cocaine self-administration when infused into either site. These findings implicate the core of NAS in the maintenance of established cocaine self-administration in trained animals, despite the fact that the reinforcement of responding in untrained animals appears to results from cocaine actions in the olfactory tubercle and medial shell and not the core of accumbens.

Acute reverse microdialysis (MD) of atropine into the pontine respiratory group (PRG) during the day has chronic affects on the control of breathing and metabolic rate

To further study the importance of acetylcholine as a neurotransmitter in the PRG, we chronically implanted microtubules into the PRG of 12 goats to assess the acute ventilatory response of reverse microdialysis (MD) of atropine (50mM) into the PRG during the day. Ipsi‐unilateral MD of atropine increased pulmonary ventilation (VI) by 6.4% (P=0.004) compared to MD of mock cerebral spinal fluid (mCSF), due to increases in both breathing frequency (P=0.042) and tidal volume (P=0.002). Unexpectedly, subsequent (2 to 4 days later) contra‐unilateral and bilateral MD of mCSF alone increased VI by 9.3% (P&lt;0.001) and 4.1% (P&lt;0.001), respectively. This change is presumed due to a carryover effect of the ipsilateral MD of atropine. Interestingly, following the increases in VI due to MD of mCSF, MD of atropine immediately attenuated these increases back to pre‐MD control levels. pH, pCO2, pO2, and body temperature were unaffected, but changes in VI were matched by changes in VO2 and VCO2, with significance on the contralateral side (P=0.015 and 0.045, respectively). These findings are consistent with previous studies where MD of atropine into the PRG of goats chronically attenuated a secondary physiologic response to hypoxia (FASEB J. 2008 22:1233.7). We conclude that MD of atropine elicits chronic effects, which subsequent MD of atropine attenuates. Supported by the Department of Veterans Affairs and NIH 25739.

Acute reverse microdialysis (MD) of atropine into the pontine respiratory group (PRG) of goats at night has no affect on breathing, but does tend to increase NREM and REM sleep

Acetylcholine is an important neurotransmitter in the PRG (Respir. Physiol. Neurobiol. 2004 Nov 15;143(2‐3):235‐49). Tonic pontine influences may have increased importance during sleep to stabilize and prevent large fluctuations in breathing. Abnormalities in this tonic facilitation, such as attenuation of cholinergic modulation (Respir. Physiol. Neurobiol. 131:135‐144, 2002.), may contribute to sleep‐disordered breathing. Accordingly, we chronically implanted microtubules into the PRG of 7 goats to assess the response of MD of atropine (50mM) into the PRG at night. MD of atropine at night did not have a significant effect on pulmonary ventilation (VI), breathing frequency, or tidal volume compared to MD of mock cerebral spinal fluid (mCSF). However, a normal state‐dependent respiratory depression was observed, where VI during REM &lt; VI during NREM &lt; VI during wakefulness. The percent of NREM and REM sleep tended to increase from the first night of ipsilateral MD, to the second night of contralateral MD, and to the third night of bilateral MD. We conclude that MD of atropine into the PRG at night does not affect breathing, but does tend to increase both NREM and REM sleep. Supported by the Department of Veterans Affairs and NIH 25739.

RETRACTED: Up-Regulation of Anterior Cingulate Cortex NR2B Receptors Contributes to Visceral Pain Responses in Rats

Electrophysiologic and behavioral studies have shown that increased N-methyl-D-aspartate (NMDA)-receptor activation of anterior cingulate cortex (ACC) neurons has a critical role in modulating visceral pain responses in viscerally hypersensitive (VH) rats. This study aimed to identify the NMDA receptor subtypes in perigenual ACC (pACC) neurons involved in the facilitation of visceral nociception. We performed in vivo electrophysiologic recordings of pACC neurons and examined the visceromotor response (VMR) to colorectal distention (CRD) in normal and VH rats induced by colonic anaphylaxis. The NR2A-subtype-receptor antagonist [(R)-[(S)-1-(4-bromo-phenyl)-ethylamino]-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-5-yl)-methyl]-phosphonic acid (NVP-AAM077) and the NR2B-receptor-antagonist Ro25-6981 were microinjected into the pACC. To down-regulate NR2B-receptor gene expression, an NR2B-specific small interfering RNA (siRNA) and a plasmid (pEGFP-N1) that expressed the green fluorescent protein were administered into ACC neurons by electroporation. Reverse microdialysis of NVP-AAM077 had no effect on basal and CRD-induced ACC neuronal firing in VH and control groups. In VH rats, Ro25-6981 (500 micromol/L) inhibited ACC neuronal firing, evoked by 30 and 50 mm Hg CRD, by 98% and 52%, respectively. NVP-AAM077 did not affect the VMR in either group. Ro25-6981 significantly suppressed the VMR in VH but not normal rats. Immunoblot analysis showed increased NR2B-receptor expression in the pACC of VH rats. NR2B siRNA-treated VH rats showed a significant reduction in the VMR, compared with controls. The NR2B subunit of the NMDA receptor has a critical role in the modulation of ACC sensitization and visceral pain responses in VH rats.

Selective inhibition of rem sleep-active pedunculopontine tegmental neurons suppresses respiratory network activity and REM sleep expression

Event Abstract Back to Event Selective inhibition of rem sleep-active pedunculopontine tegmental neurons suppresses respiratory network activity and REM sleep expression Kevin P. Grace1*, H. Liu1, 2 and Richard L. Horner1, 2 1 University of Toronto, Department of Physiology, Canada 2 University of Toronto, Department of Medicine, Canada Introduction: Rapid eye movement (REM) sleep is one of the three phenomenologically distinct and naturally occurring states of the mammalian central nervous system; associated with heightened neural activity and the inhibition of motor output pathways. During REM sleep, respiratory rate and variability are increased and the activity of certain respiratory muscles (e.g., genioglossus muscle of the tongue) is suppressed, with these changes defining the respiratory phenotype of REM sleep. Hypothesis: Based on several lines of new evidence which challenge the prevailing notion that pedunculopontine tegmental (PPT) neurons generate REM sleep, we hypothesize that selective inhibition of PPT REM sleep-active neurons will indicate that this cell group functions to suppresses REM sleep as well as shape its respiratory phenotype. Methods: This study used a combination of reverse microdialysis, electrophysiology, NADPH-diaphorase histochemistry and pharmacological methods in freely behaving rats (n=30) chronically instrumented for recording of sleep-wake states and respiratory muscle activities. Results: Bilateral perfusion of 8-OH-DPAT (10µM) into the PPT nuclei in order to selectively inhibit REM sleep-active neurons resulted in increased transitioning between sleep-wake states (P<0.001; normalized increase in transitions/hr = 76%) and a 15% reduction (P<0.001) of time spent in wakefulness predominantly accounted for by an increase in REM sleep. This increase in REM sleep propensity is reflected in the finding that the proportion of total sleep time occupied by REM sleep increased by 7.3% (P=0.017) during 8-OH-DPAT perfusion. Across all sleep-wake states, 8-OH-DPAT produced a significant increase in respiratory rate (P=0.003; mean increase = 7.3 breaths/min) and respiratory-related genioglossus activity (P=0.027; mean normalized increase = 69%). Given that a subset of PPT neurons are cholinergic, the latter effect may be due to withdrawal of direct cholinergic inhibition of the hypoglossal motor nucleus (HMN), which innervates the genioglossus muscle, since increasing endogenous acetylcholine at the HMN via microdialysis perfusion of an acetylcholinesterase inhibitor (100µM - eserine) resulted in significant suppression of respiratory-related genioglossus activity across sleep-wake states (P=0.008; mean normalized decrease = 56%). Conclusions: The PPT REM sleep-active cell population has a necessary role in shaping the phenotype of breathing via tonic suppression of respiratory rate and genioglossus muscle activity. Additionally, these neurons are critically involved in shaping sleep-wake state architecture; acting to suppress REM sleep, maintain wakefulness, and limit sleep-wake state transitioning. Current models regard the PPT nucleus as a generator of REM sleep on the basis of circumstantial evidence and therefore current models ought to be amended to reflect these direct findings. Acknowledgements: This research was supported by the CIHR K.G. is supported by a Graduate Studentship from the Ontario Thoracic Society Conference: B.R.A.I.N. platform in Physiology poster day 2009, Toronto, ON, Canada, 16 Dec - 16 Dec, 2009. Presentation Type: Poster Presentation Topic: Poster presentations Citation: Grace KP, Liu H and Horner RL (2009). Selective inhibition of rem sleep-active pedunculopontine tegmental neurons suppresses respiratory network activity and REM sleep expression. Front. Neurosci. Conference Abstract: B.R.A.I.N. platform in Physiology poster day 2009. doi: 10.3389/conf.neuro.03.2009.17.033 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: 17 Dec 2009; Published Online: 17 Dec 2009. * Correspondence: Kevin P Grace, University of Toronto, Department of Physiology, Toronto, Canada, kevin.grace@utoronto.ca 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 Kevin P Grace H. Liu Richard L Horner Google Kevin P Grace H. Liu Richard L Horner Google Scholar Kevin P Grace H. Liu Richard L Horner PubMed Kevin P Grace H. Liu Richard L Horner 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.

Local noradrenaline depletion elicits enhanced dopamine activity in the medial prefrontal cortex

Event Abstract Back to Event Local noradrenaline depletion elicits enhanced dopamine activity in the medial prefrontal cortex Rita Galosi1*, Attila Toth1, Zoltan Petyko1 and László Lénárd1 1 Hungarian Academy of Sciences , Medical School of University Pecs, Hungary Earlier data showed coupling between dopamine (DA) and noradrenaline (NA) release in the prefrontal cortex. In the present experiments, bilateral neurochemical lesions were carried out to destroy NA terminals in the medial prefrontal cortex (mPFC). In loco injection of 6-hydroxy-DOPA (6-OHDOPA) was applied. In other group, a potent DA uptake inhibitor, GBR12935 was injected before the administration of neurotoxin 6-hydroxy-dopamine (6-OHDA), which acts on both DA and NA terminal. DA and NA contents of the mPFC were determined by HPLC-electrochemical detection post mortem and in vivo. In controls, NA and DA values were 346.21 +/- 36.02 ng/g and 133.29 +/-21.61 ng/g wet weight tissue (average ± s.e.m.), respectively. GBR 12935 treatment alone did not show significant alteration in catecholamine levels. Lesions of NA terminals by 6-OHDOPA depleted the NA level only by 21 % [p<0.05]. 6-OHDOPA lesion caused elevated DA levels by 122 % [p<0.01]. Concentration of NA was reduced by 43 % [p<0.01] do to GBR 12935 + 6-OHDA lesion. The DA levels were elevated in these cases by 195 % [p<0.01]. Extracellular NA and DA concentrations were 4.36 +/- 1.03 and 5.32 +/- 0.7 pg/20μl sample, respectively. NA concentration was no detectable after GBR 12935 + 6-OHDA lesion. Baseline DA concentrations were enhanced [p<0.05]. Local reverse microdialysis of Yohimbine (10μM) α2 antagonist enhanced NA and DA level in the mPFC. Increase in DA concentration was higher following neurochemical lesion of NA terminals [p<0.01]. In summary, decreased NA input enhanced DA activity in the mPFC. This study was supported by ETT 317/2006, NKTH-OTKA K68431 and by the Hungarian Academy of Sciences. 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: Galosi R, Toth A, Petyko Z and Lénárd L (2009). Local noradrenaline depletion elicits enhanced dopamine activity in the medial prefrontal cortex. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.193 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: Rita Galosi, Hungarian Academy of Sciences , Medical School of University Pecs, Pecs, Hungary, rita.galosi@aok.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 Rita Galosi Attila Toth Zoltan Petyko László Lénárd Google Rita Galosi Attila Toth Zoltan Petyko László Lénárd Google Scholar Rita Galosi Attila Toth Zoltan Petyko László Lénárd PubMed Rita Galosi Attila Toth Zoltan Petyko László Lénárd 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.

Blocking Glutamate Receptors in the Waist Area of the Parabrachial Nucleus Decreases Taste Reactivity Behaviors in Conscious Rats

The "waist" area (W) of the parabrachial nucleus contains neurons that receive orosensory input and play a role in the initiation of oromotor behaviors. Immunohistochemical data indicate that neurons in W receive glutamatergic input and express glutamate receptors, but a behavioral role for glutamate neurotransmission within W has not been investigated. To determine the role of specific glutamate receptors in taste reactivity behaviors, glutamate receptor blockers were delivered into W by reverse microdialysis during intraoral infusion of 0.1 M sodium chloride, 0.1 M sucrose, 0.03 M hydrochloric acid, and 0.003 M quinine hydrochloride. Blocking alpha-amino-3-hydroxy-5-methyl-isoxazolepropionate (AMPA)/kainate ionotropic glutamate receptors in W with 6-cyano-7-nitroquinoxaline-2,3-dione disodium (CNQX) reduced ingestive taste reactivity behaviors to each tastant by 72-85% compared with baseline levels (P's < 0.05). Blocking N-methyl-D-aspartate receptors as well as type 1 and group III metabotropic glutamate receptors had minor effects on taste reactivity responses to the tastants. These data provide strong evidence for a behavioral role of glutamatergic neurotransmission in W in conscious rats.

Acute ethanol impairs photic and nonphotic circadian phase resetting in the Syrian hamster

Disrupted circadian rhythmicity is associated with ethanol (EtOH) abuse, yet little is known about how EtOH affects the mammalian circadian clock of the suprachiasmatic nucleus (SCN). Clock timing is regulated by photic and nonphotic inputs to the SCN involving glutamate release from the retinohypothalamic tract and serotonin (5-HT) from the midbrain raphe, respectively. Our recent in vitro studies in the SCN slice revealed that EtOH blocks photic phase-resetting action of glutamate and enhances the nonphotic phase-resetting action of the 5-HT1A,7 agonist, 8-OH-DPAT. To explore the basis of these effects in the whole animal, we used microdialysis to characterize the pharmacokinetics of intraperitoneal injection of EtOH in the hamster SCN extracellular fluid compartment and then studied the effects of such EtOH treatment on photic and serotonergic phase resetting of the circadian locomotor activity rhythm. Peak EtOH levels (approximately 50 mM) from a 2 g/kg injection occurred within 20-40 min with a half-life of approximately 3 h. EtOH treatment dose-dependently attenuated photic phase advances but had no effect on phase delays and, contrary to in vitro findings, markedly attenuated 8-OH-DPAT-induced phase advances. In a complementary experiment using reverse microdialysis to deliver a timed SCN perfusion of EtOH during a phase-advancing light pulse, the phase advances were blocked, similar to systemic EtOH treatment. These results are evidence that acute EtOH significantly affects photic and nonphotic phase-resetting responses critical to circadian clock regulation. Notably, EtOH inhibition of photic signaling is manifest through direct action in the SCN. Such actions could underlie the disruption of circadian rhythmicity associated with alcohol abuse.

Inhibition of Phosphodiesterase 10A Increases the Responsiveness of Striatal Projection Neurons to Cortical Stimulation

The cyclic nucleotide phosphodiesterase 10A (PDE10A) is highly expressed in striatal medium-sized spiny projection neurons (MSNs), apparently playing a critical role in the regulation of both cGMP and cAMP signaling cascades. Genetic disruption or pharmacological inhibition of PDE10A reverses behavioral abnormalities associated with subcortical hyperdopaminergia. Here, we investigate the effect of PDE10A inhibition on the activity of MSNs using single-unit extracellular recordings performed in the dorsal striatum of anesthetized rats. Antidromic stimulation of the substantia nigra pars reticulata was used to identify striatonigral (SNr+) MSNs. Intrastriatal infusion of the selective PDE10A inhibitors papaverine or TP-10 [2-{4-[-pyridin-4-yl-1-(2,2,2-trifluoroethyl)-1H-pyrazol-3-yl]-phenoxymethyl}-quinoline succinic acid] by reverse microdialysis did not affect spontaneous firing but robustly increased measures of cortically evoked spike activity in a stimulus intensity-dependent manner. Systemic administration of TP-10 also increased cortically evoked spike activity in a stimulus intensity- and dose-dependent manner. A robust increase in cortically evoked activity was apparent in SNr- MSNs (primarily striatopallidal). It is interesting that TP-10 administration did not affect cortically evoked activity in SNr+ MSNs. However, TP-10 administration increased the incidence of antidromically activated (i.e., SNr+) MSNs. These findings indicate that inhibition of striatal PDE10A activity increases the responsiveness of MSNs to depolarizing stimuli. Furthermore, given the lack of effect of TP-10 on SNr+ MSNs, we speculate that PDE10A inhibition may have a greater facilitatory effect on corticostriatal synaptic activity in striatopallidal MSNs. These data support further investigation of selective targeting of PDE signaling pathways in MSN subpopulations because this may represent a promising novel approach for treating brain disorders involving dysfunctional glutamatergic and dopaminergic neurotransmission.

Glycinergic and GABA(A)-mediated inhibition of somatic motoneurons does not mediate rapid eye movement sleep motor atonia.

A hallmark of rapid eye movement (REM) sleep is a potent suppression of postural muscle tone. Motor control in REM sleep is unique because it is characterized by flurries of intermittent muscle twitches that punctuate muscle atonia. Because somatic motoneurons are bombarded by strychnine-sensitive IPSPs during REM sleep, it is assumed that glycinergic inhibition underlies REM atonia. However, it has never been determined whether glycinergic inhibition of motoneurons is indeed responsible for triggering the loss of postural muscle tone during REM sleep. Therefore, we used reverse microdialysis, electrophysiology, and pharmacological and histological methods to determine whether glycinergic and/or GABA(A)-mediated neurotransmission at the trigeminal motor pool mediates masseter muscle atonia during REM sleep in rats. By antagonizing glycine and GABA(A) receptors on trigeminal motoneurons, we unmasked a tonic glycinergic/GABAergic drive at the trigeminal motor pool during waking and non-rapid eye movement (NREM) sleep. Blockade of this drive potently increased masseter muscle tone during both waking and NREM sleep. This glycinergic/GABAergic drive was immediately switched-off and converted into a phasic glycinergic drive during REM sleep. Blockade of this phasic drive potently provoked muscle twitch activity in REM sleep; however, it did not prevent or reverse REM atonia. Muscle atonia in REM even persisted when glycine and GABA(A) receptors were simultaneously antagonized and trigeminal motoneurons were directly activated by glutamatergic excitation, indicating that a powerful, yet unidentified, inhibitory mechanism overrides motoneuron excitation during REM sleep. Our data refute the prevailing hypothesis that REM atonia is caused by glycinergic inhibition. The inhibitory mechanism mediating REM atonia therefore requires reevaluation.

Endocytosis Is Required for Synaptic Activity-Dependent Release of Amyloid-β In Vivo

Aggregation of amyloid-beta (Abeta) peptide into soluble and insoluble forms within the brain extracellular space is central to the pathogenesis of Alzheimer's disease. Full-length amyloid precursor protein (APP) is endocytosed from the cell surface into endosomes where it is cleaved to produce Abeta. Abeta is subsequently released into the brain interstitial fluid (ISF). We hypothesized that synaptic transmission results in more APP endocytosis, thereby increasing Abeta generation and release into the ISF. We found that inhibition of clathrin-mediated endocytosis immediately lowers ISF Abeta levels in vivo. Two distinct methods that increased synaptic transmission resulted in an elevation of ISF Abeta levels. Inhibition of endocytosis, however, prevented the activity-dependent increase in Abeta. We estimate that approximately 70% of ISF Abeta arises from endocytosis-associated mechanisms, with the vast majority of this pool also dependent on synaptic activity. These findings have implications for AD pathogenesis and may provide insights into therapeutic intervention.

Histamine facilitates in vivo thalamocortical long‐term potentiation in the mature visual cortex of anesthetized rats

Recent evidence indicates that the mature central visual system retains a higher degree of plasticity than traditionally assumed. However, little is known regarding the neuromodulatory factors that influence plasticity in the adult primary visual cortex (V1). We investigated the role of histamine, one of the neuromodulators that densely innervate all neocortical fields, in modulating plasticity of V1 by examining thalamocortical long-term potentiation (LTP). Theta-burst stimulation of the lateral geniculate nucleus of urethane-anesthetized rats resulted in potentiation of the field postsynaptic potential recorded in the superficial layers of V1. Histamine (0.01-10 mM), applied locally in V1 by reverse microdialysis, produced a clear, dose-dependent enhancement of LTP. In addition, histamine also allowed a weak theta-burst induction protocol, that by itself failed to induce significant synaptic potentiation, to produce stable LTP. The effect of histamine to facilitate LTP was largely resistant to blockade of H(1)[chlorpheniramine, 5 and 10 mg/kg, intraperitoneal (i.p.)] or H(2) receptors (cimetidine, 10 mg/kg, zolantidine, 5 mg/kg, i.p.). However, arcaine sulfate salt (10 mg/kg, i.p.), a blocker of the polyamine binding site of the N-methyl-D-aspartate (NMDA) receptor, completely antagonized the LTP amplification induced by histamine, suggesting that it acts via a direct modulation of NMDA receptors, rather than histaminergic receptor activation. The present experiments provide the first demonstration of a histaminergic influence on neocortical synaptic plasticity in vivo and show that cortical histaminergic activation acts to lower the induction threshold and increase the degree of plasticity in the mature thalamocortical visual system.