TEMPORAL PROFILE OF TISSUE LEVELS OF DOPAMINE AND ITS METABOLITES, HVA AND DOPAC FOLLOWING FOCAL CEREBRAL ISCHAEMIA IN ANAESTHETIZED PRIMATES

Occlusion of the middle cerebral artery produced ischaemia and consequent changes in basal ganglia in the primate model of stroke within 0.5 h. Dopamine content was decreased in the right basal ganglia from 0.5 h up to 12 h after occlusion. Homovanillic acid content of the right basal ganglia increased initially at 0.5 h but, was decreased at 12 h. The DOPAC content was increased at 2 h after occlusion in the right basal ganglia, but was decreased significantly at 12 h. In the substantia nigra, there was a significant reduction in the DA content in the right side at 12 h. Minimal changes were observed in the DOPAC and HVA content in the right substantia nigra at 2 h and 4 h, respectively. At other time periods there was no significant change in the content of HVA and DOPAC in substantia nigra.     

The dynamics of dopamine metabolism in the rat superior cervical, coeliac and mesenteric ganglia

Dopamine (DA) metabolism was compared in rat superior cervical ganglion, coeliac ganglion, mesenteric ganglion and adrenal medulla. Substantial amounts of DA, 3-4 dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were found in all the above structures. The proportion of DA metabolites over total adrenergic compounds increased from the superior cervical (22 +/- 2.2%) to the mesenteric ganglia (37 +/- 1.4%) and was much higher in ganglia (30 +/- 1.6%) than in adrenal medulla (1.1 +/- 0.3%). The turnover rates of DOPAC and HVA were calculated in sympathetic ganglia after pargyline (75 mg/kg i.p.) or probenecid (200-500 mg/kg i.p.). After pargyline, the DOPAC levels decreased faster than HVA levels in all ganglia. The corresponding half-lives and calculated turnover rates were: about 4 and 10 min and 100 and 40 pmol/mg protein per h for DOPAC and HVA respectively. No differences were observed between the three ganglia. After probenecid, DOPAC accumulated in all the ganglia in a dose-dependent way; HVA accumulated in the superior cervical and coeliac ganglia but not in the mesenteric ganglion. As in central areas, the turnover rates of DOPAC and HVA calculated on the basis of the greatest accumulation of acidic levels after probenecid were much smaller than those obtained after pargyline. Probenecid increased DOPAC levels in adrenal medulla, but the concomitant changes in DA and epinephrine (E) amounts suggest that probenecid was able to enhance adrenomedullary activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

缺血预适应对沙土鼠脑缺血再灌注后纹状体多巴胺及其代谢产物的影响

目的　研究缺血预适应对沙士鼠脑缺再灌注后纹状体中多巴胺(DA)及其代谢产物的影响,以探讨其神经保护作用的可能机制。方法　应用沙土鼠脑缺血再灌注模型,脑缺血时间为 5min。96只沙土鼠随机分为假手术组 (S)、缺血组(I)、单纯预适应组 (Po)、缺血预适应组 (Ip)。在再灌注 0(即缺血末)、5、30、60min时,断头、分离纹状体,用高效液相-电化学检测器 (HPLC ECD)分别测定各组沙土鼠纹状体DA、3, 4双羟苯乙酸 (DOPAC)和高香草酸 (HVA)的含量。结果　与假手术组相比,短暂缺血组在缺血再灌注期间纹状体中DA、DOPAC和HVA含量均无显著性变化 (P>0 05)。再灌注期间,预适应、缺血再灌注组DA含量均显著低于假手术组,但在再灌注 0min和 30min时,预适应组DA含量及显著高于缺血再灌注组,分别增加了 28% (P<0 01)和 22% (P<0 05)。与假手术组相比,预适应组的DOPAC和HVA含量在再灌注期间均无显著变化 (P>0 05 );缺血再灌注组DOPAC含量在再灌注 5min时有明显增加;HVA含量在再灌注 30min时增加至峰值。结论　缺血预适应能部分抑制沙土鼠脑缺血再灌注期间纹状体DA的降低,显著减少DA氧化代谢产物的产生,从而在脑缺血再灌注损伤中起保护作用。     

Differential effects of acute and subacute HA-966 treatment on storage and release of striatal dopamine

Acute injections of HA-966 (100 mg/kg) into rats caused a rapid elevation of dopamine (DA) content in the striatum. 3,4-Dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels increased after a latency period of 0.5 h and 1 h respectively. Repeated ("subacute") HA-966 treatment produced a smaller DA increase than did single administration, while DOPAC and HVA rose at the same rate after both treatments. In HA-966-pretreated rats no tolerance for DA increase followed a lesion of the dopaminergic fibres. Acute as well as subacute HA-966 prevented the disappearance of DA after alpha-methyl-p-tyrosine for about 3 h. In both cases DOPAC and HVA levels dropped sharply after HA-966. HA-966 had no influence on the decline of DOPAC and HVA levels after monoamine oxidase inhibition. It is concluded that the rises of DOPAC and HVA after HA-966 did not occur because the capacity of the vesicular DA stores was exceeded. Instead, HA-966 affects the storage mechanism for newly formed DA. Possible explanations for the observed tolerance to DA accumulation after HA-966 are discussed.     

Regional rat brain levels of 3,4-dihydroxyphenylacetic acid and homovanillic acid: concurrent fluorometric measurement and influence of drugs

A concurrent semi-automatic fluorometric assay technique for 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), is described. The method is based on a rapid manually performed isolation of DOPAC and HVA on small columns of Sephadex G-10 followed by an automated fluorometric detection with a continuous flow system. DOPAC and HVA were measured in the corpus striatum, nucleus accumbens and olfactory tubercle of the rat, under normal conditions and after treatment with amphetamine, apomorphine, clozapine, haloperidol, morphine, oxotremorine, pargyline, probenecid, sulpiride and thioridazine. Clozapine, morphine, sulpiride and oxotremorine induced the most pronounced rise of DA metabolites in the nucleus accumbens. Probenecid produced a DOPAC accumulation in the nucleus accumbens. Striking differences were observed between the DOPAC/HVA ratios in the different structures of control animals. The concurrent assay enables a rapid screening of the action of drugs in regional DA metabolism.     

Glucocorticoid effects on mesotelencephalic dopamine neurotransmission.

Multiple neurochemical estimates were used to examine peripheral corticosterone (CORT) effects in dopaminergic terminal regions. Acute CORT administration, which elevated plasma CORT (5 h), slightly decreased dihydroxyphenylacetic acid (DOPAC) to dopamine (DA) ratios in the striatum but not in other regions examined. Two weeks of adrenalectomy (ADX) increased both medial prefrontal cortex DOPAC/DA and homovanillic acid (HVA)/DA and striatal HVA/DA. A reciprocal pattern of changes was observed with CORT replacement in ADX animals. In contrast, CORT replacement in ADX animals did not significantly influence tyrosine hydroxylase content, basal dihydroxyphenylalanine (DOPA) accumulation after NSD 1015 treatment or the decline in DA after alpha-methyl-para-tyrosine, suggesting that neither DA neuronal activity nor release are altered by CORT. Moreover, neither gamma-hydroxybutyric acid lactone-induced increases in DOPA accumulation or stress-induced increases in DA utilization were influenced by CORT replacement, indicating that neither autoreceptor regulation of DA synthesis nor acute stress regulation of DA utilization are changed by CORT. The findings are most consistent with direct inhibition of basal DA metabolism in the medial prefrontal cortex and striatum. The possible physiological and behavioral significance of this inhibition is being further explored.     

EFFECTS OF ALLOPURINOL ON STRIATAL DOPAMINE, ASCORBATE AND URIC ACID DURING AN ACUTE MORPHINE CHALLENGE: EX VIVO AND IN VIVO STUDIES

In the present studyin vivoandex vivoexperiments were combined to evaluate the effects of allopurinol on the neurochemical changes induced by an acute morphine challenge (2 mg kg⁻¹, s.c.). In samples from rat striatum, levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-methoxytyramine (3-MT), ascorbate (AA), dehydroascorbate (DHAA), hypoxanthine, xanthine and uric acid (UA) were measured. Brain microdialysis experiments were carried out in freely moving rats. Striatal dialysate levels were assayed for DA, DOPAC+HVA, AA and UA using liquid chromatography followed by electrochemical detection. Morphine administration increased the striatal levels of DA metabolites, UA and DHAA and the extracellular concentrations of DA, DOPAC+HVA, UA and AA. Allopurinol (50 mg kg⁻¹by gavage), an inhibitor of xanthine oxidase which catalyses oxidation of xanthine to UA, decreased basal UA and AA concentrations and the morphine-induced increase in DA metabolites and AA oxidation. Since oxidation of DA and xanthines generates reactive oxygen species (ROS) and AA and UA are the main cellular antioxidants, these findings suggest that: (a) single morphine administration increases DA and xanthine oxidative metabolism with a consequent increase in ROS production, which may account for changes in concentrations of extracellular AA and tissue DHAA; (b) allopurinol decreases morphine-induced DA and xanthine oxidation; (c) UA and AA may act in concert to regulate levels of ROS in the brain.     

千金藤啶碱对大鼠脑内单胺代谢的影响

1-千金藤啶碱(1-SPD 15～120 mg/kg)能增加大鼠纹状体和边缘区的多巴胺代谢物DOPAC和HVA(+150～300%),并有剂量相关关系。此作用于给药后60 min达峰值,给药后4 h虽有恢复趋势,但仍明显高于对照值。SPD还能中等度地降低上述两个脑区的DA和NA(-18～48%)。DA转换率(表现为代谢物增加)的升高支持SPD为DA受体阻断剂。但DA和NA下降表明,除有受体阻断作用外,不能排除药物对单胺递质的贮存、释放或再摄取的影响。纹状体内的5-HIAA含量亦有明显升高。     

千金藤啶碱对大鼠脑内单胺代谢的影响

1-千金藤啶碱(1-SPD 15～120 mg/kg)能增加大鼠纹状体和边缘区的多巴胺代谢物DOPAC和HVA(+150～300%),并有剂量相关关系。此作用于给药后60 min达峰值,给药后4 h虽有恢复趋势,但仍明显高于对照值。SPD还能中等度地降低上述两个脑区的DA和NA(-18～48%)。DA转换率(表现为代谢物增加)的升高支持SPD为DA受体阻断剂。但DA和NA下降表明,除有受体阻断作用外,不能排除药物对单胺递质的贮存、释放或再摄取的影响。纹状体内的5-HIAA含量亦有明显升高。     

Decrease in dopamine,its metabolites and noradrenaline in cerebrospinal fluid of schizophrenic patients after withdrawal of long-term neuroleptic treatment

Dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), noradrenaline (NA), and 5-hydroxyindolacetic acid (5HIAA) were measured in cerebrospinal fluid (CSF) of 15 chronic schizophrenic patients before and 2 weeks after withdrawal of long-term neuroleptic treatment. Total neuroleptic-like activity in serum (NLA) was determined at the same times. Levels of DA and its metabolites (DOPAC and HVA) and NA were significantly reduced after the discontinuation of neuroleptic treatment. No change was observed in 5HIAA values. NLA was substantially reduced, but still remained detectable. The decrease in DA, DOPAC, and HVA all showed positive correlations with each other, and correlated negatively with NLA measured after 2 weeks. Our data implies that the decrease in DA turnover is the result of the discontinuance of DA receptor blockade, while the change in NA level is independent of it.This work was supported by the State Office for Technical Development, Hungary     

Dual effects of nicotine on neuroleptic-induced changes of striatal dopamine metabolism in mice

The effect of nicotine on the neuroleptic-induced changes in striatal dopamine (DA) metabolism of mice was studied. To investigate the mechanism of action of nicotine, its interactions with apomorphine (APO) and gamma-hydroxybutyric acid (GHBA) were also investigated. Mice were given nicotine, (0.3-3 mg/kg subcutaneously) repeatedly (4 times) at 30 min. intervals. Haloperidol (HAL), (+/-)-sulpiride (SUL), APO or GHBA were administered after the second nicotine dose. Hexamethonium was given to prevent the effects of nicotine on autonomic ganglia. The striatal contents of DA and of its metabolites homovanillic acid (HVA), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine (3-MT) were measured. The drug-induced hypothermia in mice was controlled by increasing ambient temperature. At ambient temperature of 32-34 degrees nicotine and HAL increased the striatal DOPAC and HVA contents additively, whereas APO counteracted the effects of nicotine at this ambient temperature. At 20-22 degrees nicotine decreased the 3-MT content which indicates reduced release of DA. In hypothermic mice nicotine inhibited better the HAL- and SUL-induced increases of HVA content than those of DOPAC content suggesting that the neuroleptic-induced increases in DOPAC and HVA contents are mediated partly by different mechanisms. In APO-treated mice both the GHBA- and nicotine-induced decreases of 3-MT content fell further. GHBA did not alter the nicotine-induced decrease of 3-MT content and so this effect of nicotine may be mediated indirectly via GABAergic neurones. Unlike GHBA and APO nicotine decreased 3-MT content only in hypothermic mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

6-Hydroxydopamine and 5,7-dihydroxytryptamine selectively reduce dopamine and 5-hydroxytryptamine metabolites in cerebroventricular perfusates of rats

The efflux into the lateral cerebral ventricles of metabolites of dopamine (DA) and 5-hydroxytryptamine (5HT) was determined in unanesthetized rats bearing chronically implanted push-pull cannulae. Pretreatment with 6-hydroxydopamine (6-OHDA) reduced the basal efflux of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), but not of 5-hydroxyindoleacetic acid (5HIAA). The haloperidol-induced increase in the efflux of DOPAC and HVA was markedly attenuated in the 6-OHDA-pretreated rats. In rats treated with 5,7-hydroxytryptamine (5,7-DHT) the basal efflux of DOPAC and HVA was unaffected, while that of 5HIAA was markedly reduced; in these animals the ability of L-tryptophan to increase the perfusate content of 5HIAA was abolished. These results indicate that metabolites of DA and 5HT appearing in cerebroventricular perfusates of rats originate from DA and 5HT neuronal terminals in the brain.     

Dopaminergic toxicity of the herbicide atrazine in rat striatal slices

A possible link between Parkinson's disease and pesticide exposure has been suggested, and recently it was shown that the herbicide atrazine (ATR) modulates catecholamine metabolism in PC12 cells and affects basal ganglia function in vivo. Hence, the objectives of this study were to: (i) determine if ATR is capable of modulating dopamine (DA) metabolism in striatal tissue slices in vitro and (ii) explore possible mechanisms of its effects. Striatal tissues from adult male Sprague-Dawley rats were incubated with up to 500 microM ATR in a metabolic shaker bath at 37 degrees C and an atmosphere of 95% O(2) and 5% CO(2) for 4h. At the end of incubation, samples were collected for both tissue and media levels of DA and its metabolites (3,4-dihydroxyphenylacetic acid, DOPAC and homovanillic acid, HVA), which were determined by high-performance liquid chromatography with electrochemical detection (HPLC-ECD). To gain some mechanistic insight in to the way ATR affects DA metabolism, several pharmacological manipulations were performed. Striata exposed to ATR at concentrations of 100 microM and greater had a dose-dependent decrease of tissue levels of DA. At doses of ATR 50 microM and greater, the DOPAC+HVA/DA ratio was dose-dependently increased. Tyrosine hydroxylase (TH, the rate-limiting enzyme in DA synthesis) protein levels and activity were not affected by ATR treatment. However, high potassium-induced DA release into the medium was decreased, whereas the increase in media DA observed in the presence of the DA uptake inhibitor nomifensine was increased even further by ATR in a dose-dependent manner. All of these effects of ATR were observed at levels that were not toxic to the tissue, as LDH release into the medium (lactate dehydrogenase, an index of non-specific cytotoxicity) was not affected by ATR. Taken together, results from this study suggest that ATR decreases tissue DA levels not by affecting TH activity, but possibly by interfering with the vesicular storage and/or cellular uptake of DA.     

Effect of α-methyl fluorodopa on dopamine metabolites: Importance of conjugation and egress

The effects of D,L-α-monofluoromethyldopa (MFMD), an inhibitor of aromatic L-amino acid decarboxylase, on the metabolism of dopamine (DA) and 5-hydroxytryptamine was investigated using rat brain and cerebrospinal fluid (CSF). Vehicle or MFMD (100 mg/kg) was given p.o. and 16 h later probenecid (200 mg/kg i.p.). CSF was sampled and the rats killed immediately or after 1 h. Vehicle treated rats showed regional differences of percentage conjugation of DA metabolites: 3,4-dihydroxyphenylacetic acid (DOPAC), striatum 10%, rest of brain 45%, CSF 67%; homovanillic acid (HVA), striatum 20%, rest of brain 35%, CSF 53%. These differences and the proportionately greater increases of conjugates than of free acids after probenecid vitiate regional comparisons of DA metabolism if conjugates are not included. MFMD alone decreased neither 5HIAA (except in the striatum) nor the free DA metabolites but decreased both conjugates in CSF and conjugated DOPAC in rest of brain. The inhibitory effects of MFMD on 5HT and DA synthesis were most evident when measured by the accumulation of 5HIAA or total (DOPAC + HVA) after giving probenecid. MFMD may also inhibit amine metabolite egress and the conjugation of DOPAC and HVA.     

Release and Metabolism of Dopamine in a Clonal Line of Pheochromocytoma (PC12) Cells Exposed to Fenthion

The effects of an organophosphate (OP) pesticide, fenthion (FEN),on the release and metabolism of dopamine were evaluated ina clonal line of rat pheochromocytoma (PC 12) cells. HPLC wasused to determine media concentrations of DA and the DA metabolitesnorepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC),and homovanillic acid (HVA). The FEN formulation solvent didnot significantly affect DA metabolism. In the first study,cultures were treated with l0^–5 or l0^–6 M FEN orl0^–5 M neostigmine, a non-OP acetylcholinesterase inhibitor.Concentrations of both catecholamines were elevated in culturestreated with l0^–5 M FEN by 2.8-fold for DA and 3.5-foldfor NE. Neostigmine effects were of smaller magnitude and DAwas decreased after 24 hr. Cultures were also treated with depolarizinglevels of K⁺ but the effect of FEN was not altered, suggestingthat FEN does not act by increasing DA release. In the secondstudy, the effect of l0^–6 M FEN was evaluated in culturestreated with the DA uptake inhibitor benztropine, the monoamineoxidase (MAO) inhibitor pargyline, or the catechol-O-methyltransferase(COMT) inhibitor tropolone. Inhibitor effects were consistentwith their known mechanisms of action. In all cultures treatedwith FEN, the ratio HVA/DOPAC was decreased after 3 and 6 hrof exposure. A decrease in HVA/DOPAC was also observed in culturestreated with neostigmine and tropolone. In combination withpargyline, FEN decreased DA in contrast to its usual effectof increasing DA. Neither the stimulation of DA release northe inhibition of DA uptake affected the observed action ofFEN in PC 12 cultures. Results were supportive ofthe abilityof FEN to inhibit the catabolism of DOPAC to HVA, with a subsequentincrease in DA levels.     

Long-term effects of a priming dose and short-term infusion of amphetamine on striatal dopamine neurons in rats

A priming dose (15 mg/kg i.p.) of (+)-amphetamine sulfate combined with a 16 h subcutaneous infusion of 1.36 mg of the drug per hour to rats via its release from osmotic minipumps produced marked decreases in striatal dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and the synaptosomal uptake of [3H]DA which lasted for at least 12 weeks. The decrease in striatal DA persisted through 24 weeks after drug treatment. In contrast, striatal levels of DOPAC, HVA and synaptosomal DA uptake recovered to control levels by 24 weeks after amphetamine treatment.     

Dopamine metabolites in human brain

The relationship of human brain levels of 3,4-dihydroxyphenylacetic acid (DOPAC) to cerebrospinal fluid levels of this dopamine (DA) metabolite was studied. The effect of postmortem delay was evaluated in the rat. DOPAC was resistant to postmortem changes in brain kept in situ. The level of DOPAC (free and conjugated) determined in DA-rich areas of six human brains amounted to only a fraction of the homovanillic acid (HVA) found in the same regions. The DOPAC/HVA ratio in human brain was similar to that found in CSF. We conclude that HVA is the major DA metabolite in human brain and that DA metabolite levels in CSF reflect DA metabolite levels in brain.     

Acute and chronic effects of neuroleptics and acute effects of apomorphine and amphetamine on dopamine turnover in corpus striatum and substantia nigra of the rat brain

The effects of chronic neuroleptic treatment on the concentrations of homovanillic acid (HVA) and 3,4-dihydroxy-phenylacetic acid (DOPAC) in the rat substantia nigra (SN) and corpus striatum (CS) were determined. Acute haloperidol and alpha-flupenthixol increased HVA and DOPAC in the CS but after chronic treatment no significant change was found compared to controls. In the SN, on the contrary, acute haloperidol reduced and subsequently increased HVA and DOPAC and alpha-flupenthixol had no significant effect, whereas chronic treatment with either neuroleptic increased the levels of the metabolites. Acute apomorphine reduced HVA and DOPAC in CS, but increased first and subsequently decreased the levels of the metabolites in the SN. Acute amphetamine reduced both metabolites in SN and DOPAC in CS, whereas striatal HVA was unaffected. The different or even reciprocal effects on DA release may suggest an independent local action of these drugs in CS and SN.     

Effect of low-dose sulpiride on dopamine metabolism in rat nucleus accumbens and locomotor activity: studies with intracerebral dialysis]

Changes in the concentration of dopamine (DA) and its metabolites, 3, 4-dihydroxyphenyl-acetic acid (DOPAC) and homovanillic acid (HVA), were determined sequentially in freely moving rats by using a brain dialysis method. The purpose of this study was to investigate the relationship between changes in the dopamine metabolism in the nucleus accumbens and locomotor activities following low-dose (5 mg/kg) sulpiride administration. The DA content in the dialysis fluid rose significantly 4 to 6 h after sulpiride administration. The DOPAC content rose significantly 6 h after sulpiride administration. The HVA content did not show a significant change. A slight increase of locomotor activity was found, but it was not statistically significant. The elevation of DA release in nucleus accumbens by sulpiride might relate to the clinical efficacy of low-dose administration of this drug for mood disorders.     

Study of the turnover or the release of brain dopamine in rats after administration of N-linoleyl dopamine]

Wistar male rats received N-linoleyl dopamine (L-DA) at doses of 10, 50 or 100 mg/kg (i.p.). 2 h after these injections they were decapitated and dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), as well as the ratio DOPAC/DA, which could represent the DA turnover, were determined in the striatum, the frontal cortex or the hypothalamus, while homovanillic acid (HVA) as well as the ratio HVA/DA, which could represent the DA release, were determined in the striatum by high performance liquid chromatography (HPLC). Except a small rise of DA and DOPAC in the hypothalamus, at high L-DA doses, no significant modifications in DA, DOPAC, DOPAC/DA, HVA or HVA/DA were observed in the other brain areas studied. These results, in good agreement with the recent data obtained with other dopaminergic agonists, could show the absence of correlation between the hypomotility, on the one hand and the decreasing of the turnover or the release of the brain DA, on the other hand. Together with the data obtained recently by scandinavian and italian authors, they could raise questions about the position and the role of dopaminergic autoreceptors.