Responsiveness of Striatal Dopamine Release in Awake Animals After Chronic 1-Methyl-4-Phenylpyridinium Ion-Induced Lesions of the Substantia Nigra

Extracellular concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid were measured by microdialysis in rat striatum 1 month after a unilateral infusion via a dialysis probe of a high concentration (10 mM) of 1-methyl-4-phenylpyridinium ion (MPP+) into the substantia nigra. The basal extracellular DA concentration at the lesioned side was about 20% of the concentration at the nonlesioned side. However, basal DOPAC dialysate levels from the lesioned striatum represented only 2.4% of those from the contralateral side. Intrastriatal infusion with nomifensine increased the dialysate content of DA about twofold and eightfold at the lesioned and nonlesioned sides, respectively. Co-infusion of nomifensine with (-)-sulpiride caused an additional pronounced rise of the DA output on top of the nomifensine-induced increase at the nonlesioned side, whereas no effect was observed at the lesioned side. Finally, MPP+ (10 mM) was infused for 45 min into both striata. The increase in the dialysate content of DA in response to MPP+ (considered as an index of the total striatal DA content) from the lesioned side was only 0.6% of the MPP(+)-induced DA increase from the nonlesioned side. A strong compensatory response to increased extracellular dopamine was observed in the ipsilateral striatum. This effect was achieved by a severe suppression of reuptake mechanisms, as well as of the autoreceptor feedback response. It is concluded that infusion of MPP+ into the substantia nigra can be used as a chronic biochemical model for clinically manifest parkinsonism.     

Intracerebral Dialysis and the Blood-Brain Barrier

Abstract: The aim of the study was to evaluate how implantation of a dialysis probe influences the blood-brain barrier. Leakage of endogenous serum albumin was evaluated by Evans blue/albumin staining and by immunohistochemistry. The passage from blood to dialysate of two substances that normally do not pass into the brain, [³H]inulin and glutamate, was studied 3 and 24 h after insertion of a dialysis probe. Evans blue, given 20 min before rats were killed, was observed around the probe and surrounding brain tissue. Albumin immunoreactivity was seen at considerable distance from the probe with larger spread at 24 h than at 3 h after probe insertion. Glutamate and [³H]inulin were detected in the dialysate with no significant further increase of radioactivity after intracarotid infusion of protamine sulfate that enhances the permeability over the blood-brain barrier. When protamine was followed by infusion of glutamate, the concentrations of taurine increased in the dialysate in four of eight rats. That plasma constituents have access to the brain around the dialysis probe is essential to consider, particularly in studies using substances and drugs that do not pass an intact blood-brain barrier.     

In Vivo Mechanisms Underlying Dopamine Release from Rat Nigrostriatal Terminals: II. Studies Using Potassium and Tyramine

The brain microdialysis technique has been used to examine the in vivo effects of potassium and tyramine on dopamine (DA) release and metabolism in the striatum of halothane-anaesthetised rats. Increasing the concentration of potassium perfusing the dialysis probe (30-120 mM) induced a dose-related efflux of DA. A dose-related release of DA was also observed following addition of tyramine (1-100 microM) to the perfusing buffer. High concentrations of potassium were found to reduce the dialysate content of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid and the serotonin metabolite 5-hydroxyindoleacetic acid. No such effect was observed even when using the highest concentration of tyramine tested. Potassium-evoked DA release was facilitated by pretreatment with the DA uptake inhibitor nomifensine, was inhibited by depletion of extracellular calcium, and was not significantly affected by tetrodotoxin (TTX). The effect of tyramine on DA efflux was inhibited by nomifensine and was insensitive to both TTX and calcium depletion. These data suggest that potassium and tyramine induce release of DA via different mechanisms. Potassium-induced DA release involves a carrier-independent process and may utilise an exocytotic release mechanism. On the other hand, tyramine-induced DA release would appear to involve a carrier-dependent process. Depletion of vesicular stores of DA by pretreatment with reserpine did not significantly affect potassium-induced DA release, whereas a marked inhibition of the effects of tyramine was noted. However, in reserpinised animals the potassium-induced release of DA was inhibited by nomifensine, a result suggesting that a carrier-dependent release mechanism operates in the absence of vesicular DA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of extracellular 5-HT and 5-HIAA in hippocampus of freely moving rats using microdialysis: long-term applications

Extracellular levels of 5-hydroxytryptamine (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured in the ventral hippocampus of the awake rat using microdialysis. The basal level of 5-HT in hippocampal dialysates was very close to the detection limit of our assay. However, addition of a 5-HT re-uptake blocker, citalopram, to the perfusion medium resulted in a 3-fold rise of 5-HT levels in dialysates and provided a stable baseline. Under these conditions, extracellular levels of 5-HT and 5-HIAA could be measured up to 11 days after dialysis probe implantation. 5-HT measured in dialysate was Ca²⁺-dependent both 24 h and 7 days after surgery. In comparison K⁺-induced depolarization caused a 9-fold increase in 5-HT output 24 h after probe implantation and this effect had disappeared 10 days later, although behavioral activation following K⁺ application was similar 24 h and 11 days after surgery. Systematic administration of -trytophan had no significant effect on 5-HT but increased 5-HIAA levels by 90%. These results suggest that in the presence of citalopram, 5-HT in hippocampal dialysates is derived from serotonergic neurones. The microdialysis method appears most useful for measurement of extracellular 5-HT 24–72 h after probe implantation. Finally, our data indicate that extracellular 5-HIAA mainly reflects intraneuronal metabolism of 5-HT prior to release.     

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.     

Corticotropin-Releasing Factor Stimulates Catecholamine Release in Hypothalamus and Prefrontal Cortex in Freely Moving Rats as Assessed by Microdialysis

Abstract: In vivo microdialysis was used to measure changes in extracellular concentrations of catecholamines and indoleamines in freely moving rats in response to administration of corticotropin-releasing factor (CRF). Dialysis probes were placed stereotaxically in either the medial hypothalamus or the medial prefrontal cortex. We used a repeated-measures design in which each rat received artificial CSF or one dose of CRF 3–4 h apart, and each subject was retested with the same treatments in the reverse order 5–7 days later. With the dialysis probe in the hypothalamus, intracerebroventricular administration of CRF (17 or 330 pmol) dose-dependently increased dialysate concentrations of norepinephrine (NE), dopamine (DA), and all their measurable catabolites except normetanephrine. The effects on NE were substantially greater than those on DA. Dialysate concentrations of serotonin could not be measured reliably, but those of its catabolite, 5-hydroxyindoleacetic acid, were also elevated. Concentrations of NE and DA were elevated within the first one or two (20 min) collection periods, with a peak response at ∼ 1–2 h. Dialysate concentrations of catecholamines and metabolites normally returned to baseline within 3 h. Similar data were obtained with dialysis probes in the medial prefrontal cortex after intracerebroventricular administration of 17 or 167 pmol of CRF, except that the increases in DA exceeded those of NE in this region. Intraperitoneal administration of CRF (1 nmol) similarly elevated dialysate concentrations of NE, DA, 5-hydroxyindoleacetic acid, and all catecholamine catabolites except normetanephrine in both medial hypothalamus and medial prefrontal cortex. These results support earlier neurochemical data suggesting that CRF administered both centrally and peripherally stimulates the release of both DA and NE in the brain.     

Fixed Versus Removable Microdialysis Probes for In Vivo Neurochemical Analysis: Implications for Behavioral Studies

Abstract: The levels of several neurochemicals, i.e., uric acid (UA), dopamine (DA), dihydroxyphenylacetic acid, and 5-hydroxyindoleacetic acid, collected daily from the rat striatum with either fixed or removable microdialysis probes for 7 days after surgery were compared. The implantation of the fixed cannula was followed by a 10-fold increase in the UA content in the dialysates collected from the first day after surgery onward and by a steady decrease in dihydroxyphenylacetic acid levels, whereas those of DA remained fairly stable. With the removable cannula system, only a smaller, transient increase in UA during the first 3 days after surgery was observed, with no change in DA or monoamine metabolites. The glial reaction around the cannula tracks was assessed by both quantitative histological techniques and measuring the glutamine levels in the dialysates collected at the time of surgery and 7 days later. Both the glial cell number and nuclear size, as well as the glutamine outflow, were considerably larger in the animals implanted with the fixed probes. It is, therefore, likely that the UA levels in the dialysate reflect the glial reaction to the probe. The suitability of the removable probe system for behavioral experiments involving repeated microdialysis sampling was illustrated in an experiment showing that the DA release in the nucleus accumbens of male rats assessed daily at postsurgery days 5–10 was virtually identical in three alternating sessions of sexual behavior as was the smaller release of this neurotransmitter detected during intervening nonsexual social interactions.     

Effect of Transient Cerebral Ischaemia and Cardiac Arrest on Brain Extracellular Dopamine and Serotonin as Determined by In Vivo Dialysis in the Rat

The effects of 20-min transient, global, forebrain ischaemia and cardiac arrest on extracellular concentrations of dopamine (DA), serotonin (5-HT), and their respective metabolites, homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), were measured in vivo by dialysis of rat striatum and hippocampus. During the ischaemic period, striatal DA content increased (250-fold basal concentrations) with parallel but much less marked increases of both striatal and hippocampal 5-HT content (eight- to 10-fold). Baseline values were restored during reperfusion. Subsequent increases of DA and 5-HT levels on cardiac arrest were comparable after both sham operation and ischaemia. Significant decreases of HVA and 5-HIAA levels were observed following ischaemia or cardiac arrest. The differential effects of ischaemia on DA and 5-HT suggest selective alterations in disposition or metabolism of the two transmitters and that dopaminergic neurones may be more vulnerable to ischaemic insults.     

Effect of Tryptophan on Extracellular Concentrations of Tryptophan and 5-Hydroxyindoleacetic Acid in the Striatum and Cerebellum

The effects of L-tryptophan (50 mg/kg i.p.) on extracellular concentrations of tryptophan and the 5-hydroxytryptamine (5-HT) metabolite 5-hydroxyindoleacetic acid (5-HIAA) were determined in the rat striatum and cerebellum, regions with rich and poor 5-HT innervation, respectively. Determinations were on perfusates from dialysis probes in the brains of conscious, freely moving rats. The pharmacokinetic profiles of dialysate tryptophan after tryptophan load (peak concentration, time to peak concentration, area under curve, and half-life) in the two regions did not differ significantly. The dialysate 5-HIAA concentration in the striatum rose two- to threefold after the administration of tryptophan. Therefore, as 5-HIAA was undetectable in the cerebellum either before or after the administration of tryptophan, the increase of 5-HIAA in the striatum is unlikely to depend appreciably on its production within the cerebral vasculature or outside the brain or on its entering the striatum through a blood-brain barrier damaged by placement of the dialysis probe. Overall, the findings strengthen previous evidence that extracellular 5-HIAA concentrations determined by cerebral dialysis are a valid measure of the metabolism of 5-HT of brain neuronal origin.     

Effects of endotoxin and tumor necrosis factor alpha on regional brain neurotransmitters in mice

Alterations in regional brain concentration of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their metabolites were investigated in male BALB/c mice injected intraperitoneally with bacterial lipopolysaccharide (LPS, 2 mg kg(-1)) or recombinant murine tumor necrosis factor alpha (TNFalpha, 0.1 mg kg(-1)) at 2, 6, 12 and 24 h after the injection. At 2 h post-injection the LPS administration resulted in hypothermia, which was not apparent at later time points. No consistent effects were observed by either LPS or TNFalpha on peripheral leukocyte counts or plasma transaminase levels. Both LPS and TNFalpha slightly elevated NE metabolism in the striatum at 2-12 h. Concentrations of DA and its metabolites were significantly elevated only in the hypothalamus following TNFalpha at 24 h. Tumor necrosis factor alpha exerted pronounced effects on 5-HT metabolism in most brain regions at 2 h. Results suggest that the effect of LPS is more complex compared with TNFalpha because of the endogenous production of other cytokines including the TNFalpha.     

Effect of Varying the Ionic Concentration of a Microdialysis Perfusate on Basal Striatal Dopamine Levels in Awake Rats

In vivo microdialysis was used to study the effects of Ca2+, Mg2+, and K+ ion concentrations on basal extracellular (EC) levels of striatal DA and metabolites in awake rats on the second day (48 h) after implantation of a microdialysis probe. Basal EC striatal dopamine (DA) levels were markedly (90%) and reversibly reduced by removal and subsequent replacement of Ca2+ ions from the microdialysis perfusate. This implies that the EC DA in this preparation is primarily of synaptic origin. The addition and subsequent removal of 1.7 mM MgCl2 to the Mg2(+)-free perfusate produced a reversible decrease (20%) in basal EC DA levels. This decrease may reflect a competitive interaction between Ca2+ and Mg2+ in the process of vesicular release. Basal EC DA levels were also reduced (27%) by decreasing the K+ concentration of the perfusate from 4 mM to 3 mM. However, after restoring the K+ concentration to 4 mM, EC DA levels were slow to return to pretreatment levels. Basal EC 3,4-dihydroxyphenylacetic acid and homovanillic acid levels exhibited a parallel but diminished response to each manipulation of the ionic concentration of the perfusate. This study demonstrates that small variations in the concentrations of Ca2+, Mg2+, and K+ in the perfusate employed in microdialysis preparations will affect basal EC striatal DA and metabolite levels.     

Intracerebrally administered (6r)-l-erythro-tetrahydrobiopterin does not affect extracellular levels of dopamine and serotonin metabolites in rat striatum in vivo during measurement by brain micro-dialysis system

By the use of the brain micro-dialysis technique combined with HPLC, the changes in the extracellular levels of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and a serotonin(5-HT) metabolite, 5-hydroxyindoleacetic acid (5-HIAA) were examined in the rat striatum before and after intracerebral injection of a vehicle or (6R)-l-erythro-tetrahydrobiopterin (6R-BH₄), the natural form of the cofactor for the tryrosine hydroxylase and tryptophan hydroxylase. No apparent change after the 6R-BH, treatment was found in the levels of DA, DOPAC, HVA and 5-HIAA in the striatal dialysate. In contrast, the levels of total biopterin in both the operated (dialysis probe-implanted) and unoperated striatum of 6R-BH₄-treated rats increased by 23- and 93-fold, respectively, when compared with those of the control, vehicle-treated rats. The results indicate that increased levels of the tetrahydrobiopterin cofactor may not affect the release of DA and the extracellular level of DA and 5-HT metabolites in the physiologically normal brain.     

Effect of Ethanol on Extracellular Dopamine in Rat Striatum by Direct Perfusion with Microdialysis

Abstract: The concentration-related effects of ethanol on extracellular dopamine (DA) in rat striatum were studied by direct perfusion through microdialysis probes in freely moving rats. Two sets of three ethanol concentrations were separately tested using a Latin square experimental design. Potassium stimulation with high potassium (50 m M ) in artificial CSF (ACSF) preceding ethanol treatment confirmed the neuronal function of dopaminergic cells by increasing DA concentrations to 200–1,500% of basal levels. The perfusion with calcium-free ACSF applied at the end of each experiment confirmed the calcium dependency of the basal levels of extracellular DA by decreasing basal DA levels by 70%. The striatal volume measurement to examine the possible brain damage by direct ethanol perfusion suggested that ethanol did not increase the damage caused by the probe implantation at any ethanol concentration tested in this study. The 30-min direct perfusion of 510 and 860 m M ethanol resulted in a significant concentration-related stimulatory effect on the extracellular DA concentration in rat striatum (510 m M , 29% increase, p < 0.05; 860 m M , 66% increase, p < 0.05). However, there was no significant effect of ethanol at low concentrations, ≤170 m M . Considering the effective ethanol concentration in tissue areas in which DA is sampled, the data suggest that concentrations of ethanol associated with moderate intoxication do not directly affect the extracellular concentration of DA in the striatum. Therefore, the systemic effects of ethanol on striatal DA found in previous studies may be caused by the interaction with sites other than the striatum.     

Extracellular Striatal Dopamine and Its Metabolites During Transient Cerebral Ischaemia

Severe cerebral ischaemia has been repeatedly shown to provoke a massive increase in striatal extracellular dopamine (DA). These experiments were undertaken to determine the duration of the DA increase produced by transient ischaemia, and the fate of the released DA during recirculation. Experiments were performed in anaesthetised rats subjected to 20 min of cerebral ischaemia, followed by 80 min of reperfusion, before cardiac arrest. Measurements of catechols were made in the striatum using in vivo differential pulse voltammetry (DPV), each 4 min, throughout the experiment and for 60 min after cardiac arrest. DPV data were substantiated with intracerebral dialysis; 20-min dialysate samples were analysed for DA and homovanillic acid (HVA) using HPLC. In 6 of 11 rats, ischaemia induced a massive DA release in the striatum, resulting in a marked increase in extracellular levels (350-1,200%), which persisted throughout ischaemia. DPV and intracerebral dialysis demonstrated that DA was totally cleared from the extracellular space within minutes of reperfusion, whereas both its acidic metabolites (3,4-dihydroxyphenylacetic acid and HVA) increased slightly. These results indicate that DA released during 20-min ischaemia is rapidly cleared during reperfusion, mainly via reuptake. In the five other rats, only a relatively small and transient increase in the DPV catechol peak was detectable, cleared before the end of ischaemia, probably reflecting less severe ischaemia; small or no changes were detectable in the corresponding dialysate. The latter data suggest that different change(s) in the nigrostriatal dopaminergic system may occur, according to the severity of ischaemia.     

Striatal Tissue Preparation Facilitates Early Sampling in Microdialysis and Reveals an Index of Neuronal Damage

Abstract: Injury-induced efflux of dopamine was compared between two microdialysis preparations. Rats were implanted with guide cannulae 5–10 days prior to microdialysis experiments. In one group, ventral striatal tissue was punctured with stainless steel obturators that remained in place until the day of the experiment. In the other group, the tissue was not punctured until the microdialysis probes were inserted. Rats from each group were dialyzed with calcium-free artificial extracellular fluid or tetrodotoxin 4 h after probe insertion. In the rats with previously punctured tissue, calcium depletion reduced dialysate dopamine concentrations to 8% of baseline. Dialysis with tetrodotoxin reduced dopamine concentrations to less than 1% of baseline. In the rats with freshly punctured tissue, dopamine concentrations were reduced only to 50% of baseline levels by calcium depletion and to 30% during dialysis with tetrodotoxin. Thus, penetration of the tissue prior to testing can significantly reduce the acute injury-induced efflux of dopamine. Further, a significant correlation was found between baseline 3,4-dihydroxy-phenylacetic acid/dopamine ratios and the efficacy of tetrodotoxin in reducing dialysate dopamine concentrations. Thus, basal 3,4-dihydroxyphenylacetic acid/dopamine ratios appear to provide an index of the amount of injury-induced dopamine efflux following probe insertion.     

Influence of Potassium Concentration in Microdialysis Perfusate on Basal and Stimulated Striatal Dopamine Release: Effect of Ceruletide, a Cholecystokinin-Related Peptide

Abstract: The in vivo microdialysis method was used to study the effect of the cholecystokinin-related peptide, ceruletide, on extracellular levels of dopamine (DA) in the striatum following perfusion with various K⁺ concentrations. Increasing the K⁺ concentration in the perfusate from 4 to 15 or 17.5 m M did not change basal DA release or release evoked by electrical stimulation of the medial forebrain bundle (MFB). However, when the perfusing solution contained 20 or 30 m M K⁺, dose-dependent reductions of both basal and MFB-stimulated DA release occurred. Subcutaneous administration of ceruletide at 160 μg/kg had no influence on the basal or MFB-stimulated DA release with 4 or 15 m M K⁺ in the perfusate. However, after perfusion with 17.5 m M K⁺, ceruletide significantly attenuated the basal and MFB-stimulated DA release. Carbachol (10 μ M ) locally applied via the dialysis probe also attenuated MFB-stimulated DA release after perfusion with 17.5 m M K⁺. From these results, we conclude that under appropriate depolarization of striatal DA terminals, ceruletide induces further depolarization and inactivation of nigrostriatal DA terminals. The present data suggest that this effect may be mediated via intrinsic cholinergic neurons in the striatum.     

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.     

The effects of pH on amphetamine-induced dopamine release as measured by in vivo dialysis

The release of endogenous dopamine (DA) from the rat corpus striatum before and after the administration of d-amphetamine sulphate (AMPH) was monitored by in vivo dialysis to compare the effects of perfusion media at pH 6.0 and at pH 7.4. Basal release of DA did not differ significantly at pH 6.0 (61.25 +/- 5.34 pg/sample, n = 4) or pH 7.4 (58.02 +/- 14.17 pg/sample, n = 4). The basal value of homovanillic acid (HVA) was not significantly reduced at pH 7.4 as compared with pH 6.0; while there was a significant reduction in 3,4-dihydroxyphenylacetic acid (DOPAC) at pH 7.4 as compared to pH 6.0. Intraperitoneal injection of 2.5 mg/kg AMPH resulted in a 21 fold increase in the concentration of DA appearing in subsequent dialysis samples. This increase in DA release was not significantly affected by the pH. Equally the decrease in DOPAC and HVA content following AMPH were also not altered by the pH. These present results differ from experiments using push-pull cannulae and suggest that responses observed with the two techniques may not be equivalent.     

Enhancement of 3,4-methylenedioxymethamphetamine neurotoxicity by the energy inhibitor malonate

The acute and long-term effects of the local perfusion of 3,4-methylenedioxymethamphetamine (MDMA) and the interaction with the mitochondrial inhibitor malonate (MAL) were examined in the rat striatum. MDMA, MAL or the combination of MAL with MDMA was reverse dialyzed into the striatum for 8 h via a microdialysis probe while extracellular dopamine (DA) and serotonin (5-HT) were measured. One week later, tissue immediately surrounding the probe was assayed for DA and 5-HT tissue content. Local perfusion of MDMA increased DA and 5-HT release but did not produce long-term depletion of DA or 5-HT in tissue. Malonate also increased both DA and 5-HT release but, in contrast to MDMA, produced only long-term depletion of DA. The combined perfusion of MDMA/MAL synergistically increased the release of DA and 5-HT and produced long-term depletion of both DA and 5-HT in tissue. These results support the conclusion that DA, compared with 5-HT, neurons are more susceptible to mitochondrial inhibition. Moreover, MDMA, which does not normally produce DA depletion in the rat, exacerbated MAL-induced DA depletions. The effect of MDMA in combination with MAL to produce 5-HT depletion suggests a role for bio-energetic stress in MDMA-induced toxicity to 5-HT neurons. Overall, these results highlight the importance of energy balance to the function of DA and 5-HT neurons and to the toxic effects of MDMA.     

Halothane attenuated haloperidol and enhanced clozapine-induced dopamine release in the rat striatum

The effect of halothane anesthesia on changes in the extracellular concentrations of dopamine (DA) and its metabolites (3-methoxytyramine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA)) induced by neuroleptics was studied using in vivo microdialysis techniques. Halothane attenuated haloperidol-induced dopamine release and enhanced clozapine-induced dopamine release in the rat striatum.A microdialysis probe was implanted into the right striatum of male SD rats. Rats were given saline or the same volume of 200 microg kg(-1) haloperidol (D(2) receptor antagonist), 10 mg kg(-1) sulpiride (D(2) and D(3) antagonist), or 10 mg kg(-1) clozapine (D(4) and 5-HT(2) antagonist) intraperitoneally with or without 1-h halothane anesthesia (0.5 or 1.5%). Halothane anesthesia did not change the extracellular concentration of DA, but increased the metabolite concentrations in a dose-dependent manner. The increased DA concentration induced by haloperidol was significantly attenuated by halothane anesthesia, whereas the metabolite concentrations were unaffected. Halothane had no effect on the changes in the concentrations of DA or its metabolites induced by sulpiride. The clozapine-induced increases in DA and its metabolites were enhanced by halothane anesthesia.Our results suggest that halothane anesthesia modifies the DA release modulated by antipsychotic drugs in different ways, depending on the effects of dopaminergic or serotonergic pathways.