Endothelin-3 modification of dopamine release in anaesthetised rat striatum; an in vivo microdialysis study.

Endothelin-3 (ET-3), a member of the vasoconstrictive peptide family, has recently been recognized as a neuropeptide. We used brain microdialysis and on-line HPLC to examine the effect of ET-3 on the basal outflow of monoamines and their metabolites in the ketamine-anaesthetised rat striatum in vivo. Although intrastriatal infusion of ET-3 (40 pmol/rat) did not change basal dopamine (DA) release, after perfusion of DA releasing agent (5 x 10(-5) M ouabain or 120 mM KCl), ET-3 could increase the DA level. Further, these effects of ET-3 were attenuated by calcium-free Ringer. These data indicated that ET-3 may act by modifying the exocytosis from the striatum of rat brain to enhance DA release after depolarization induced by an agent such as KCl or ouabain.     

7-Nitroindazole enhances amphetamine-evoked dopamine release in rat striatum. an in vivo microdialysis and voltammetric study.

The intracellular second messenger nitric oxide (NO) is implicated in a variety of physiological functions, including release and uptake of dopamine (DA). In the described study, in vivo microdialysis and differential pulse voltammetric techniques were used to determine the involvement of NO in release of DA and its metabolites (dihydroxyphenylalanine, DOPAC; homovanillic acid, HVA) in neostriatum of freely moving rats. While the NO donor molsidomine (30.0 mg/kg; MOLS) and neuronal NO synthase- (nNOS-) inhbitor 7-nitroindazole (10.0 mg/kg; 7-NI) had no effect on the basal in vivo microdialysate level of DA, 7-NI specifically enhanced D,L-amphetamine-(1.0 mg/kg i.p.; AMPH) evoked release of DA. Basal or AMPH effects on DOPAC and HVA levels were not influenced by MOLS or 7-NI. Findings indicate that nitrergic systems have an important role in mediating effects of AMPH on dopaminergic systems.     

Propentophylline increases striatal dopamine release but dampens methamphetamine-induced dopamine dynamics: A microdialysis study

While there are currently no medications approved for methamphetamine (METH) addiction, it has been shown that propentofylline (PPF), an atypical methylxanthine, can suppress the rewarding effects of methamphetamine (METH) in mice. This experiment studied the interactions of PPF with METH in striatal dopaminergic transmission. Herein, the impact of PPF (10–40 mM, intrastriatally perfused (80 min) on the effect of METH (5 mg/kg, i.p.) on striatal dopamine (DA) release was evaluated using brain microdialysis in Sprague–Dawley adult rats. METH was injected at the 60 min time point of the 80 min PPF perfusion. The extracellular levels of DA and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined using high performance liquid chromatography with electrochemical detection (HPLC-ED). PPF induced a concentration-dependent increase in DA release beginning 30 min after the onset of PPF perfusion. DA peak levels evoked by 40 mM PPF were similar to those induced by 5 mg/kg METH i.p. Only the highest concentration of PPF decreased the METH-induced DA peak (circa 70%). The significant decreases in extracellular levels of DOPAC and HVA evoked by METH were partially blocked by 10 and 20 mM PPF. Although 40 mM of PPF also partially blocked the METH-induced DOPAC decrease, it completely blocked HVA depletion after a transient increase in HVA levels in METH-treated rats. Data indicates for the first time that while PPF increases presynaptic striatal DA dynamics it attenuates METH-induced striatal DA release and metabolism.     

Ketanserin pretreatment attenuates MDMA-induced dopamine release in the striatum as measured by in vivo microdialysis

Systemic administration of the amphetamine analogue, 3,4-methylenedioxymethamphetamine (MDMA) produced a dose-dependent increase in the extracellular concentration of dopamine (DA) in the striatum as measured by in vivo microdialysis in awake, freely-moving rats. The extracellular concentration of the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), was significantly decreased in dialysate samples following the administration of MDMA (10 and 20 mg/kg, i.p.). The serotonin-2 (5-HT2) antagonist ketanserin (3 mg/kg, i.p.) had no effect on the extracellular concentration of DA or DOPAC in the striatum of vehicle- treated rats. The administration of ketanserin (3 mg/kg) 1 hr prior to MDMA (20 mg/kg) significantly attenuated the MDMA- induced increase in the extracellular concentration of DA without affecting the decrease in DOPAC concentrations. These data are suggestive that MDMA administration increases DA release in the striatum of awake, freely-moving rats. In addition, MDMA-induced increase in the extracellular concentration of DA in the striatum is mediated, in part, via 5-HT2 receptor mechanisms.     

Suppression of nigrostriatal and mesolimbic dopamine release in vivo following noradrenaline depletion by DSP-4: a microdialysis study.

Pretreatment of rats with the noradrenergic neurotoxin DSP-4 selectively reduced regional levels of noradrenaline in the brain by more than 75%, and decreased the concentration of endogenous DA in microdialysates of the caudate nucleus and nucleus accumbens by 52% and 28%, respectively. Results support the hypothesis that central noradrenergic mechanisms facilitate nigrostriatal and mesolimbic dopamine transmission in vivo.     

NMDA-mediated release of glutamate and GABA in the subthalamic nucleus is mediated by dopamine: an in vivo microdialysis study in rats

The present study investigated the effects of N-methyl-D-aspartic acid.H2O (NMDA) on the dopamine, glutamate and GABA release in the subthalamic nucleus (STN) by using in vivo microdialysis in rats. NMDA (100 micromol/L) perfused through the microdialysis probe evoked an increase in extracellular dopamine in the STN of the intact rat of about 170%. This coincided with significant increases in both extracellular glutamate (350%) and GABA (250%). The effect of NMDA perfusion on neurotransmitter release at the level of the STN was completely abolished by co-perfusion of the selective NMDA-receptor antagonist MK-801 (10 micromol/L), whereas subthalamic perfusion of MK-801 alone had no effect on extracellular neurotransmitter concentrations. Furthermore, NMDA induced increases in glutamate were abolished by both SCH23390 (8 micromol/L), a selective D1 antagonist, and remoxipride (4 micromol/L), a selective D2 antagonist. The NMDA induced increase in GABA was abolished by remoxipride but not by SCH23390. Perfusion of the STN with SCH23390 or remoxipride alone had no effect on extracellular neurotransmitter concentrations. The observed effects in intact animals depend on the nigral dopaminergic innervation, as dopamine denervation, by means of 6-hydroxydopamine lesioning of the substantia nigra, clearly abolished the effects of NMDA on neurotransmitter release at the level of the STN. Our work points to a complex interaction between dopamine, glutamate and GABA with a crucial role for dopamine at the level of the STN.     

Modulation of ventral pallidal dopamine and glutamate release by the intravenous anesthetic propofol studied by in vivo microdialysis

Summary. The intravenous anesthetic propofol is reported to have various psychological side effects as hallucinations, sexual disinhibition, or euphoria. Hedonic and rewarding states like these are modulated by the dopaminergic system in the nucleus accumbens, prefrontal cortex and also in the ventral pallidum and by the glutamatergic system in the neocortex and limbic system. In the present study, propofol was administered either alone or in combination with the GABAA receptor antagonist bicuculline via reverse microdialysis into the ventral pallidum of freely moving rats. Dialysis fractions were taken every 20min and analyzed for dopamine and glutamate using high performance liquid chromatography. Application of propofol decreased dopamine levels in the ventral pallidum. This effect seems to be mainly mediated through GABAA receptors, since it was compensated by the GABAA receptor antagonist bicuculline. Propofol and propofol plus bicuculline exerted no effect on glutamate release in this brain region. The reduced dopamine release in ventral pallidum was most probably mediated through a GABAergic feedback loop from the ventral pallidum via the nucleus accumbens to the dopaminergic neurons of the ventral tegmental area or by long loop feedback. As an increase but not a decrease of dopamine release in the ventral pallidum is involved in hedonic and rewarding properties, similar symptoms induced by propofol seem to be unrelated to an action of propofol in the ventral pallidum.     

Isoflurane anesthesia inhibits clozapine- and risperidone-induced dopamine release and anesthesia-induced changes in dopamine metabolism was modified by fluoxetine in the rat striatum: an in vivo microdialysis study

Previously, we have reported that halothane anesthesia increases the extracellular concentrations of dopamine (DA) metabolites in the rat striatum using in vivo microdialysis techniques, and we have suggested that volatile anesthetics affect DA release and metabolism in various ways. The present investigation assesses the effect of isoflurane, widely used in clinical anesthesia, on DA release and metabolism. A microdialysis probe was implanted in the striatum of male Sprague-Dawley rats (n=5-7 per group). After recovery, the probe was perfused with modified Ringer's solution and 40 microl of dialysate were injected into a high performance liquid chromatograph every 20 min. The rats were given saline or the same volume of 10 mg kg(-1) clozapine, risperidone, fluoxetine or citalopram. After the pharmacological treatment, the rats were anesthetized with 1.0% or 2.5% isoflurane for 1h. The data were analyzed using two-way analysis of variance (ANOVA). For each drug with significant (p<0.05) drug-time interactions, the statistical analysis included one-way ANOVA and Newman-Keuls post hoc comparisons. A high concentration of isoflurane (2.5%) anesthesia increased the extracellular concentration of DA metabolites during emergence from anesthesia. The levels of DA metabolites increased in an isoflurane concentration-dependent manner. Isoflurane attenuated DA release induced by clozapine and risperidone. Fluoxetine, but not citalopram, antagonized the isoflurane-induced increase in metabolites. The results of current investigation suggest that isoflurane enhances presynaptic DA metabolism, and that the oxidation of DA might be partially modulated by the activities of the dopaminergic-serotonergic pathway at a presynaptic site in the rat striatum.     

Somatostatin stimulates striatal acetylcholine release by glutamatergic receptors: an in vivo microdialysis study

The modulation of striatal cholinergic neurons by somatostatin (SOM) was studied by measuring the release of acetylcholine (ACh) in the striatum of freely moving rats. The samples were collected via a transversal microdialysis probe. ACh level in the dialysate was measured by the high performance liquid chromatography method with an electrochemical detector. Local administration of SOM (0.1, 0.5 and 1 microM) produced a long-lasting and concentration-dependent increase in the basal striatal ACh output. The stimulant effect of SOM was antagonized by the SOM receptor antagonist cyclo(7-aminopentanoyl-Phe-D-Trp-Lys-Thr[BZL]) (1 microM). In a series of experiments, we studied the effect of 6,7-dinitroquinoxaline-2, 3-dione (DNQX), a selective non-NMDA (N-methyl-D-aspartate) glutamatergic antagonist, on the basal and SOM-induced ACh release from the striatum. DNQX, 2 microM, perfused through the striatum had no effect on the basal ACh output but inhibited the SOM (1 microM)-induced ACh release. The non-NMDA glutamatergic receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylendioxy-5H-2,3- benzodiazepine (GYKI-52466), 10 microM, antagonized the SOM (1 microM)-induced release of ACh in the striatum. Local administration of the NMDA glutamatergic receptor antagonist, 2-amino-5-phosphonopentanoic acid (APV), 100 microM, blocked SOM (1 microM)-evoked ACh release. Local infusion of tetrodotoxin (1 microM) decreased the basal release of ACh and abolished the 1 microM SOM-induced increase in ACh output suggesting that the stimulated release of ACh depends on neuronal firing. The present results are the first to demonstrate a neuromodulatory role of SOM in the regulation of cholinergic neuronal activity of the striatum of freely moving rats. The potentiating effect of SOM on ACh release in the striatum is mediated (i) by SOM receptor located on glutamatergic nerve terminals, and (ii) by NMDA and non-NMDA glutamatergic receptors located on dendrites of cholinergic interneurones of the striatum.     

NMDA-induced 45Ca release in the dentate gyrus of newborn rats: in vivo microdialysis study

This in vivo study, aimed at detecting the N-methyl-D-aspartate (NMDA) evoked Ca(2+)-induced Ca(2+) release from intracellular stores in the neonatal rat brain, demonstrates that the application of 5 mM N-methyl-D-aspartate via a microdialysis probe for 20 min to the dentate gyrus (DG) of halotane-anesthetized 7 day-old (postnatal day 7, PND 7) rats induces a prolonged decrease in Ca(2+) concentration in an initially calcium-free dialysis medium, indicative of a drop in the extracellular concentration of Ca(2+) and Ca(2+) influx to neurons. In parallel experiments, a huge NMDA-evoked release of 45Ca from the pre-labeled endogenous Ca(2+) pool was observed and interpreted as the expression of intracellular Ca(2+) release. Dantrolene (100 microM) significantly inhibited the NMDA-induced 45Ca release, whereas 250 microM ryanodine exerted an unspecific biphasic effect. Autoradiographic and immunocytochemical detection of ryanodine receptors and calbindin D(28K), respectively, in the hippocampal region of PND 7 rats displayed a pronounced expression of [3H]ryanodine binding sites in the DG, but only a slight immunoreactivity of calbindin D(28K). Plastic changes in neurons or excitotoxic neuronal damage induced by the activation of NMDA receptors are mediated by Ca(2+) signals, resulting from an influx of extracellular Ca(2+), and also in some neurons, from the release of intracellular Ca(2+). Our previous in vivo microdialysis experiments visualized NMDA-evoked 45Ca release in the adult rat dentate gyrus, attributable to Ca(2+)-induced Ca(2+) release from the ryanodine-sensitive pool. An additional role of calbindin in the mechanism of this phenomenon has been suggested. This aspect has not been studied in vivo in newborn rats. Our present results indicate that the release of 45Ca from the prelabeled intracellular, dantrolene-sensitive Ca(2+) pool in the DG neurons of immature rats, most probably representing a phenomenon of Ca(2+)-induced Ca(2+) release, significantly participates in the generation of NMDA receptor-mediated intracellular Ca(2+) signals, whereas the role of calbindin D(28K) in the mechanism of 45Ca release is negligible.     

Effects of CGP 28014 on the in vivo release and metabolism of dopamine in the rat striatum assessed by brain microdialysis

The effects on rat striatal dopamine (DA) metabolism of systemic and local administration of CGP 28014, an inhibitor of catechol-O-methyl-transferase (COMT), were studied by in vivo microdialysis. CGP 28014 (30 mg/kg i.p.) significantly reduced the levels of homovanillic acid (HVA), but did not modify DA and 3,4-dihydroxyphenylacetic acid (DOPAC). The intrastriatal administration (via the microdialysis probe) of 5, 7.5, 10, and 20 mM of CGP 28014 elicited a concentration-dependent, several-fold increase in extracellular DA but did not alter the levels of HVA and DOPAC. Thus, the effects of CGP 28014 observed after i.p. injection (decrease in HVA levels) are different from those measured after intrastriatal administration (increase in DA release). Therefore, the inhibition of COMT is likely to be due to the action of a metabolite of CGP 28014 formed in the periphery and not in the brain.     

An in vivo microdialysis coupled with liquid chromatography/tandem mass spectrometry study of cortisol metabolism in monkey adipose tissue

It is postulated that elevated tissue concentrations of cortisol may be associated with the development of metabolic syndrome, obesity, and type 2 diabetes. The 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) enzyme regenerates cortisol from inactive cortisone in tissues such as liver and adipose. To better understand the pivotal role of 11β-HSD1 in disease development, an in vivo microdialysis assay coupled with liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis using stable isotope-labeled (SIL) cortisone as a substrate was developed. This assay overcomes the limitations of existing methodologies that suffer from radioactivity exposure and analytical assay sensitivity and specificity concerns. Analyte extraction efficiencies (E_d) were evaluated by retrodialysis. The conversion of SIL-cortisone to SIL-cortisol in rhesus monkey adipose tissue was studied. Solutions containing 100, 500, and 1000 ng/mL SIL-cortisone were locally delivered through an implanted 30-mm microdialysis probe in adipose tissue. At the delivery rate of 1.0 and 0.5 μL/min, E_d values for SIL-cortisone were between 58.7 ± 5.6% (n = 4) and 72.7 ± 1.3% (n = 4), whereas at 0.3 μL/min E_d reached nearly 100%. The presence of 11β-HSD1 activities in adipose tissue was demonstrated by production of SIL-cortisol during SIL-cortisone infusion. This methodology could be applied to cortisol metabolism studies in tissues of other mammalian species.     

Highly sensitive chromatographic assay for dopamine determination during in vivo cerebral microdialysis in the rat

A highly sensitive, yet simple, isocratic high-performance liquid chromatographic (HPLC) assay with electrochemical detection (ED) for the determination of extracellular dopamine (DA) in brain microdialysates is presented. The method makes possible the detection of less than 100 pM (less than 1 fmol on column) and the quantitation of 200 pM (2 fmol on column) of DA with the use of a narrow-bore rather than capillary or microbore column. Analysis is feasible within an 11-min run-time, and thus is suitable for the relatively short sampling intervals used in microdialysis experiments. In the calibration range of 0.2 to 10 nM, the method has excellent linearity and precision, with intra-day relative standard deviations (RSD) of 0.5-2.4% and between-day RSD of 2.1-4.3%.     

Ovarian steroids and hypothalamic norepinephrine release: studies using in vivo brain microdialysis

This study employed microdialysis in urethane-anesthetized female rats to monitor ovarian steroid-dependent changes in KCl-evoked levels of extracellular norepinephrine (NE) in the ventromedial hypothalamus. An initial KCl stimulus (Sl) increased NE from low or undetectable levels in all animals. A second KCl stimulus (S2) given several hr later evoked 40% less NE release than did Sl in ovariectomized (OVX) females or OVX females given only estrogen or progestin. In contrast, the two KCl-evoked NE releases were equivalent in OVX females administered both estrogen and progestin. These results suggest that ovarian steroids may act as presynaptic modulators of NE release in the ventromedial hypothalamus.     

Hypoxia-mediated in vivo release of dopamine in nucleus tractus solitarii of rabbits

A wide variety of neuroactive substances have been suggested to be involved in the respiratory depression observed in response to severe hypoxia. By use of the technique of microdialysis, the release of dopamine (DA) was measured in the nucleus tractus solitarii during severe hypoxic provocations (6% O2 in N2) in the adult pentobarbital-anesthetized rabbit. DA release was analyzed by high-performance liquid chromatography with electrochemical detection. Such hypoxic provocations caused pronounced phase of depression in the phrenic nerve activity and enhanced release of DA. After bilateral carotid sinus nerve denervation, acute severe hypoxia did not give rise to enhanced release of DA or to phrenic nerve depression. Mild hypoxic (9% or 12% O2 in N2) or hypercapnic (6% CO2) stimuli resulted in an increased phrenic nerve activity without any concomitant changes in DA release. Decerebration at the midcollicular level in rabbits prevented an enhanced release of DA in the nucleus tractus solitarii during severe hypoxia. The results suggest that 1) DA is involved in the central ventilatory response to severe hypoxia, 2) not only the initial excitatory but also the second depressive phase in response to severe hypoxia is mediated partially by the peripheral chemoreceptors, and 3) the depressive phase is dependent on intact connections from suprapontine structures.     

Application of in vivo microdialysis to the study of cholinergic systems

The application of in vivo microdialysis to the study of acetylcholine (ACh) release has contributed greatly to our understanding of cholinergic brain systems. This article reviews standard experimental procedures for dialysis probe selection and implantation, perfusion parameters, neurochemical detection, and data analysis as they relate to microdialysis assessments of cholinergic function. Particular attention is focused on the unique methodological considerations that arise when in vivo microdialysis is dedicated expressly to the recovery and measurement of ACh as opposed to other neurotransmitters. Limitations of the microdialysis technique are discussed, as well as methodological adaptations that may prove useful in overcoming these limitations. This is followed by an overview of recent studies in which the application of in vivo microdialysis has been used to characterize the basic pharmacology and physiology of cholinergic neurons. Finally, the usefulness of the microdialysis approach for testing hypotheses regarding the cholinergic systems' involvement in cognitive processes is examined. It can be concluded that, in addition to being a versatile and practical method for studying the neurochemistry of cholinergic brain systems, in vivo microdialysis represents a valuable tool in our efforts to better comprehend ACh's underlying role in a variety of behavioral processes.     

Amphetamine-stimulated release of endogenous dopamine from the rat caudate nucleus in vivo

The in vivo release of endogenous dopamine (DA) has been measured from the rat caudate nucleus. A push-pull cannula was implanted into the brain and the tissue was perfused with artificial cerebrospinal fluid (CSF) containing amphetamine in concentrations ranging from 5 X 10(-3) to 5 X 10(-7) M. The DA released into the perfusate was determined by a radioenzymatic procedure. DA release was increased to levels significantly above its resting rate by amphetamine concentrations of 5 X 10(-6) M or greater. Release stimulated by 5 X 10(-5) M amphetamine was significantly reduced by removing calcium from the perfusing fluid; the unstimulated release rate was not significantly affected. The concentrations of amphetamine required to increase DA release in vivo would appear to be similar to those found in the brain following intraperitoneal doses which produce increases in locomotor activity and stereotyped behavior.     

Mechanism of action of methylmercury on in vivo striatal dopamine release. Possible involvement of dopamine transporter

Methylmercury (MeHg) produces significant increases in the spontaneous output of dopamine (DA) from rat striatal tissue. The mechanism through MeHg produces such increase in the extracellular DA levels could be due to increased DA release or decreased DA uptake into DA terminals. One of the aims of this study was to investigate the role of DA transporter (DAT) in the MeHg-induced DA release. Coinfusion of 400 microM MeHg and nomifensine (50 microM) or amphetamine (50 microM) produced increases in the release of DA similar to those produced by nomifensine and amphetamine alone. In the same way, MeHg-induced DA release was not attenuated under Ca(2+)-free conditions or after pretreatment with reserpine (10 mg/kg i.p.) or tetrodotoxin (TTX), suggesting that the DA release was independent of calcium and vesicular stores, as well as it was not affected by the blockade of voltage sensitive sodium channels. Thus, to investigate whether depolarization of dopaminergic terminal was able to affect MeHg-induced DA release, we infused 75 mM KCl through the dialysis membrane. Our results clearly showed a decrease induced by MeHg in the KCl-evoked DA release. Taken together, these results suggest that MeHg induces release of DA via transporter-dependent, calcium- and vesicular-independent mechanism and it decreases the KCl-evoked DA release.     

Studies,using in vivo microdialysis,on the effect of the dopamine uptake inhibitor GBR 12909 on 3,4-methylenedioxymethamphetamine ('ecstasy')-induced dopamine release and free radical formation in the mouse striatum

The present study examined the mechanisms by which 3,4-methylenedioxymethamphetamine (MDMA) produces long-term neurotoxicity of striatal dopamine neurones in mice and the protective action of the dopamine uptake inhibitor GBR 12909. MDMA (30 mg/kg, i.p.), given three times at 3-h intervals, produced a rapid increase in striatal dopamine release measured by in vivo microdialysis (maximum increase to 380 +/- 64% of baseline). This increase was enhanced to 576 +/- 109% of baseline by GBR 12909 (10 mg/kg, i.p.) administered 30 min before each dose of MDMA, supporting the contention that MDMA enters the terminal by diffusion and not via the dopamine uptake site. This, in addition to the fact that perfusion of the probe with a low Ca(2+) medium inhibited the MDMA-induced increase in extracellular dopamine, indicates that the neurotransmitter may be released by a Ca(2+) -dependent mechanism not related to the dopamine transporter. MDMA (30 mg/kg x 3) increased the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) from salicylic acid perfused through a probe implanted in the striatum, indicating that MDMA increased free radical formation. GBR 12909 pre-treatment attenuated the MDMA-induced increase in 2,3-DHBA formation by approximately 50%, but had no significant intrinsic radical trapping activity. MDMA administration increased lipid peroxidation in striatal synaptosomes, an effect reduced by approximately 60% by GBR 12909 pre-treatment. GBR 12909 did not modify the MDMA-induced changes in body temperature. These data suggest that MDMA-induced toxicity of dopamine neurones in mice results from free radical formation which in turn induces an oxidative stress process. The data also indicate that the free radical formation is probably not associated with the MDMA-induced dopamine release and that MDMA does not induce dopamine release via an action at the dopamine transporter.