In vivo microdialysis studies of age-related alterations in potassium-evoked overflow of dopamine in the dorsal striatum of Fischer 344 rats

Intracerebral microdialysis was used to measure basal levels and potassium (K(+))-stimulated overflow of dopamine (DA), homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC), in the dorsal striatum of young (6 months) and aged (24 months) Fischer 344 (F344) rats. Basal levels of HVA were lower in aged rats whereas basal DA and DOPAC did not differ significantly between the two groups. The administration of three low to moderate doses of K(+) (10, 25, and 50 mM) through the microdialysis probe for one collection period revealed differences between the two age groups of F344 rats. DA overflow increased in a dose-dependent manner in the young but not aged rats. Extracellular levels of DOPAC and HVA decreased during the K(+) stimulation and there was a significant difference in the changes in HVA produced by K(+) stimulation in the young vs aged animals. These data support the hypothesis that low to moderate doses of K(+) may be necessary to demonstrate age-related differences in K(+)-evoked DA overflow, since previous microdialysis studies using higher doses have not reported age-related differences in DA overflow.     

Metabolism of monoamine neurotransmitters in the evolution of infarction in ischemic striatum

Summary The time course of changes in monoamine metabolism in ischemic striatum was assessed by measurement of levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT) and 5-hydroxy-indole-acetic acid (5-HIAA) 2, 4, 7 and 16 hours after irreversible unilateral carotid ligation in Mongolian gerbils with stroke. DA was reduced to 30% of the level in the contralateral non-ischemic striata by 2 hours after stroke, but DOPAC was significantly elevated (p < 0.01) to 227%, while HVA remained equal to control. At 4 hours after stroke, DOPAC was 86% of the contralateral non-ischemic striata but HVA had risen to 130%. At 7 hours after stroke, DOPAC in the ischemic striata was 148% of control, while HVA remained at 133%. By 16 hours after stroke, DA, DOPAC and HVA were depleted from the ischemic striata, corresponding to the time course for irreversible damage to the neurotransmitter uptake function of nerve terminals. 5-HT levels in the ischemic striata were 30% of control at 2 hours, 46% at 4 hours, 30% at 7 hours and 21% at 16 hours, while 5-HIAA remained equal to control throughout the time course. These studies indicate that monoamine metabolism continues in ischemic striatum for up to 8 hours after the onset of stroke following irreversible unilateral carotid ligation in the Mongolian gerbil, but metabolism of DA is disrupted by 16 hours after stroke while metabolism of 5-HT continues.     

Peripheral distribution of free dopamine and its metabolites in the rat

Summary Free dopamine (DA) and its metabolites, homovanillic acid (HVA) and 3–4 dihydroxyphenylacetic acid (DOPAC), have been measured and compared with norepinephrine (NE) concentrations in rat peripheral tissues using high performance liquid chromatography with electrochemical detection (HPLC-ED). Detectable amounts of DA and its metabolites were found in all the analyzed tissues. The highest levels were found in carotid body, sympathetic ganglia, urogenital tract and heart, the lowest in liver and lung. DA and DOPAC distribution was heterogeneous and unrelated to NE concentration. Both the variable value of the DA/DA+NE ratio and the presence of DA metabolites in peripheral tissues indicate that a portion of DA may be stored outside noradrenergic neurons and directly catabolized in specific DA pools.     

Evidence for dopamine as a transmitter in dorsal hippocampus

Intrahippocampal distribution of dopamine (DA) and its metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), was studied along with those of noradrenaline (NA) and 5-hydroxytryptamine in rats. DA concentration in the dorsal part of the hippocampus was found to be 4–10 times higher than in other parts. A study of metabolite distributions produced similar results, showing a higher concentration in the dorsal part of the hippocampus. A ratio of NA/DA had a value similar to that of the hypothalamus in which apparent dopaminergic innervation has been reported. Haloperidol decreased the DA level, whereas it increased the concentration of metabolites, in whole and dorsal hippocampus. The ratio HVA/DOPAC increased after haloperidol treatment. These findings strongly suggest the presence of dopaminergic innervation in at least the dorsal part of the hippocampus.     

Treadmill running combined with microdialysis can evaluate motor deficit and improvement following dopaminergic grafts in 6-OHDA lesioned rats

To evaluate the physiological role of striatal dopamine (DA) during exercise and the mechanism of functional recovery mediated by grafted DAergic neurons, the locomotor ability (treadmill running) and DA turnover were investigated using treadmill running combined with in vivo microdialysis in the intact control rats, 6-hydroxydopamine (6-OHDA) lesioned rats (hemi-parkinsonian model rats) and DAergic cell grafted rats. The 3 groups of rats were trained to run on a straight treadmill at a speed of 1,800 cm/min for 20 min every day for 7 consecutive days. If the rats could not follow the speed they got electrostimulation (ES) from the grid behind the treadmill belt. The numbers of ES rats received during treadmill running were counted to quantify the locomotor ability. Control rats could keep up with the treadmill easily (0-1 ES/10 min), whereas lesioned rats could not follow the speed (80-100 ES/10 min). Most of the grafted rats received only a few ES, but a few received over 100 ES/10 min. Extracellular DA and its metabolites, dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA), were measured by in vivo microdialysis and high-performance liquid chromatography (HPLC) during and after treadmill running. In control rats the basal levels of DA, DOPAC and HVA were 2.3 fmol/μl, 1,109.8 fmol/μl and 612.2 fmol/μl, respectively. They increased up to 130%, 140% and 160% by running. In 6-OHDA lesioned rats basal values of DA, DOPAC and HVA were less than 10% of controls. We did not perform microdialysis in these rats since they got too much ES during running. In grafted rats that showed good recovery in locomotor ability, DA returned to almost control level (1.9 fmol/μl), but those of DOPAC (127.8 fmol/μl) and HVA (100.2 fmol/μl) were still low. DA, DOPAC and HVA increased up to 130%, 130% and 150% by running in a similar pattern as in intact rats. These results suggest that grafted neurons can release and metabolize DA in the host striatum both tonically and phasically in relation with internal and external stimuli and also suggest that treadmill running ability is a good indicator of DA turnover in the striatum. Thus, the treadmill running test with microdialysis is useful for quantitative evaluation of motor function in grafted animals.     

Effects of 250 mg% ethanol on monoamine and amino acid release from rat striatal slices

A single IP injection of 2.5 g ethanol/kg body weight into the rat increased the striatal levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) one hour later to 133 and 141% of control values, respectively. Blood alcohol concentrations at this time were approximately 250 mg%. The increased striatal tissue levels of DOPAC and HVA found after IP administration did not appear to be due to a direct effect of ethanol on the efflux of these two metabolites or on the release of dopamine (DA) since in vitro studies with striatal slices demonstrated that 250 mg% ethanol had no effect on the endogenous release of DOPAC, HVA, or DA. However, ethanol did enhance the K+-stimulated, Ca2+-dependent release of glutamate and aspartate from striatal slices to 168 and 214% of control values, respectively. The release of glutamate and aspartate from slices of midbrain (minus colliculi) was also increased by 250 mg% ethanol. On the other hand, the release of GABA, NE and 5-HT did not appear to be significantly altered by 250 mg% ethanol. The in vitro findings have led to the hypothesis that the elevated DOPAC and HVA levels observed in the striatum following an acute IP injection of 2.5 g/kg of ethanol are due to increased release of DA produced by the excitatory actions of glutamate (and/or aspartate) on dopaminergic neurons.     

Age influences abnormalities in striatal dopamine metabolism during and after transient forebrain ischemia

Summary Age has been found to be a significant risk factor for brain ischemia and its mortality. After cerebral ischemia, the nigrostriatal dopaminergic system undergoes selective vulnerability with necrosis of striatal neurons. To study the effect of age and transient forebrain ischemia on striatal dopamine metabolism, investigations were performed in 1-year-old (adult) and 2-year-old (aged) male Wistar rats. A 15 min period of bilateral transient incomplete ischemia (ICI) was induced, and the concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), and homovanillic acid (HVA) were measured in the striatum by means of HPLC and electrochemical detection at the end of ischemia without reperfusion, and after 1h, 24h, 72h, 144h, and 288h of postischemic cerebral reperfusion.In normal conditions, no 3-MT was detectable in either age group studied, and no other age-related changes could be found in DA or its metabolites. During ICI, an age-related difference became obvious in the 3-MT concentration, which was higher in aged animals. In this group, DOPAC dropped and DA turnover increased. After 1 h of postischemic reperfusion, the concentrations of DOPAC and HVA, as well as the turnover rate, had increased in both age groups, whereas an increase in the DA concentration became apparent in the adult animals only. The enhancement of the concentration of both DOPAC and HVA was more marked in adult animals than in aged ones. At 24h of postischemic cerebral reperfusion, DA concentration was still elevated in both age groups, and HVA in the 1-year-old animals only. At 72h of postischemic cerebral reperfusion, no differences were obvious between adult experimental animals and controls, whereas the elevated DA concentration persisted in aged animals, being higher than in the control group and in the 1-year-old rats. DA turnover was reduced. Longer periods of postischemic cerebral reperfusion were not found to be followed by any abnormalities compared with controls except for the DA concentration at 288h (1-year-old group); nor were there any differences between the two age groups studied.The data obtained in this investigation clearly indicate age-related differences in the striatal dopaminergic neurotransmission after transient cerebral ischemia, in that in the aged brain reactions are markedly delayed after an injurious event such as ischemia.     

Acute effects of intranigral application of MPP+ on nigral and bilateral striatal release of dopamine simultaneously recorded by microdialysis.

Intracerebral microdialysis in freely moving rats was used to investigate the effects of perfusions with the 1-methyl-4-phenylpyridinium ion (MPP+) in the substantia nigra (SN) on the extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in the perfused SN and in the ipsi- and contralateral striata. Following MPP+ perfusion, the release of DA in the SN increased markedly from nondetectable basal levels to about 105 fmoles/min, whereas the output of DOPAC, HVA and 5-HIAA decreased below 25% of basal levels. The intranigral MPP+ application induced, at the same time, an almost immediate, long-lasting decrease in the release of DA in the ipsilateral striatum to less than 20% of basal levels and a moderate increase in the DOPAC and HVA levels, without affecting 5-HIAA output. In the contralateral striatum, the extracellular levels of DA, DOPAC, HVA and 5-HIAA remained unchanged during the entire perfusion experiment. These results suggest that infusion of 10 mM MPP+ into the SN produces an almost immediate blockade of neuronal impulse flow, as shown by the rapid decline in DA release from the ipsilateral striatal nerve terminals. The simultaneously occurring massive increase of the extracellular DA in the SN is, therefore, probably the result of destruction of the nigral cell bodies and/or dendrites following locally applied MPP+. This study clearly illustrates the possibilities of simultaneous microdialysis in various brain areas, allowing pharmacological manipulations on the levels of the cell bodies, while monitoring events in the terminal areas.     

Microdialysates of amines and metabolites from core nucleus accumbens of freely moving rats are altered by dizocilpine

In vivo microdialysis combined with high performance liquid chromatography (HPLC) with electrochemical detection, was used to study the effect of MK-801 (0.1 mg/kg i.p.) on extracellular concentrations of dopamine (DA) 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), norepinephrine (NE) and DOPAC/DA ratio in intact, 6-hydroxydopamine (6-OHDA)-lesioned, DSP4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzyl-amine hydrochloride)-lesioned and reserpine-treated rats. The results revealed high basal DA (0.735+/-0.05 fmol/microl), DOPAC (195.93+/-20.18 fmol/microl) and NE (0.585+/-0.01 fmol/microl), low 5-HT (0.334+/-0.032 fmol/microl) and high DOPAC/DA ratio (265.11+/-20.73) in intact cACC. 6-OHDA alone (8 microg/2 microl) depleted DA (-66%), DOPAC (-65%), and NE (-62%). On the other hand, in desipramine (DMI)-pretreated rats, 6-OHDA induced a large depletion of DA (-94%), DOPAC (-97%) and reduced DOPAC/DA ratio (-73%), but increased NE to 142% of intact and 369% of 6-OHDA-lesioned rats. DSP4 (50 mg/kg) decreased NE (-97%), DOPAC (-75%) and DOPAC/DA ratio (-69%). Reserpine (5 mg/kg s.c.) significantly decreased DOPAC (-84%), DOPAC/DA ratio (-81%), 5-HT (-69%) and NE (-86%), but nonsignificantly increased DA. In the intact rats, MK-801 did not change DA, but increased DOPAC and DOPAC/DA ratio. In 6-OHDA-lesioned rats, MK-801 increased DA, whereas in 6-OHDA+DMI rats MK-801 additionally increased DOPAC and DOPAC/DA ratio. DSP4 and reserpine reduced the ability of MK-801 to increase DOPAC and DOPAC/DA ratio. MK-801 did not change NE concentration in dialysates collected from intact rats, but increased that from 6-OHDA+DMI-lesioned rats. In DSP4-lesioned and reserpine-treated rats, MK-801 increased NE but to a level lower than that observed in the intact rats. These results suggest that systemic administration of a low dose of MK-801, which induces profound locomotor stimulation without stereotypy, increases DOPAC and DOPAC/DA ratio in the cACC of intact rats, whereas it additionally increases the depleted DA and NE concentrations especially in 6-OHDA-lesioned rats pretreated with DMI.     

Simultaneous HPLC quantification of monoamines and metabolites in the blood-free rat cochlea

Monoamine quantification in peripheral sensory receptors, such as the cochlea, is of major interest since monoamines could play a role in neurotransmission. A three-step biochemical protocol was developed to analyze monoamine content within the cochlea. Removal of the blood by aortic perfusion was carried out with an anticoagulant solution prior to the dissection of the cochlea from the temporal bone. The cochlear monoamines and some of their metabolites were then quantified, from homogenated cochlear tissue, by a new application of high performance liquid chromatography coupled to electrochemical detection. This method demonstrated enough sensitivity to detect norepinephrine (NE), dopamine (DA), serotonin (5-HT) and some of their metabolites (3,4-dihydroxyphenylacetic acid, DOPAC; homovanillic acid, HVA; and 5-hydroxyindole-3-acetic acid, 5-HIAA). Furthermore, it enabled the demonstration of noise-induced changes in the cochlear concentrations of NE, DA, DOPAC and HVA. In addition, the aortic perfusion allowed removal of the blood-borne 5-HT from the cochlea without inducing systemic alterations or monoamine degradation, as shown by the absence of effects on NE, DA, DOPAC, HVA or 5-HIAA concentrations. The present methodology may constitute a useful strategy to analyze monoamine turnover in the cochlea and other peripheral sensory receptors.     

Ceruletide suppresses endogenous dopamine release via vagal afferent system, studied by in vivo intracerebral dialysis

Ceruletide, a cholecystokinin-related decapeptide, has been reported to have some therapeutic effects on tardive dyskinesia and other involuntary movement disorders. In order to clarify the effects of ceruletide on dopaminergic activity in the rat striatum, we measured the release of endogenous dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) after intraperitoneal administration of ceruletide (2, 20, 200 micrograms/kg) using in vivo intracerebral dialysis techniques. After administration of ceruletide (200 micrograms/kg), extracellular DA decreased significantly (P less than 0.05) for 0.5-3 h. The maximal reduction of extracellular DA (by 29%) was observed for 2-2.5 h. Extracellular DA was reduced (21%) by 20 but not by 2 micrograms/kg ceruletide. DOPAC and HVA did not change at any dose of ceruletide. We also demonstrated that bilateral subdiaphragmatic vagotomy blocked this inhibitory effect of ceruletide on DA release. These findings indicate that peripherally administered ceruletide suppresses endogenous DA release via the vagal afferent system.     

Effect of chronic naltrexone administration and its withdrawal on the regional activity of neurons that contain norepinephrine, dopamine and serotonin

A method is described that permits the simultaneous quantitation of norepinephrine (NE), dopamine (DA) serotonin (5-HT) and their respective major metabolites, 3-methoxy-4-hydroxy phenylglycol (MHPG), 3-methoxytyramine (3-MT), dihydroxyphenyl acetic acid (DOPAC) and 5-hydroxyindole acetic acid (5-HIAA) in discrete brain regions. The ratio of MHPG/NE, DOPAC/DA and 5-HIAA/5-HT was used to assess the effects of the chronic administration of the narcotic antagonist, naltrexone, and its withdrawal on the regional activity of neurons that contain NE, DA and 5-HT respectively. Chronic administration of naltrexone (8 days) is associated with a significant increase in the ratio of 5-HIAA/5-HT and DOPAC/DA in the frontal cortex and dorsal hippocampus respectively. Under this condition the thalamic concentration of 3-MT in 4 of 8 animals is also significantly elevated. In contrast, the mesolimbic forebrain exhibited a decrease in the MHPG/NE ratio (4 out of 8 animals). One day following naltrexone pellet removal the above ratios, as well as the mean content of 3-MT in the thalamus, returned to control values. At this time the content of 3-MT in the thalamus (5 of 5 animals) and frontal cortex (3 of 9 rats) was appreciably elevated, while its content in the dorsal hippocampus was significantly reduced (6 of 9 rats). These data suggest that the activity of several central monoaminergic neuronal systems are regulated by an opioid input that is tonically active.     

Dose related effects of 6-OHDA on rabbit retinal dopamine concentrations and ERG B-wave amplitudes

The purpose of this study was to examine the dose related effects of 6-hydroxydopamine (6-OHDA) on the electroretinographic (ERG) B-wave amplitude and on retinal concentrations of dopamine (DA) and its main metabolites homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC). Doses of 6-OHDA (60, 300 or 1200 micrograms) were dissolved in a 0.9 percent NaCl and ascorbic acid solution and administered intravitreally in 300 microliter volume in one eye of adult pigmented rabbits. The fellow eye received a similar volume of the drug vehicle. With the smallest dose of 6-OHDA (60 micrograms) no changes in ERG B-wave amplitude or retinal concentrations of DA, DOPAC or HVA were found. With the largest dose of 6-OHDA (1200 micrograms) complete extinction of the ERG and almost total disappearance of DA, DOPAC and HVA were observed. With the intermediate dose of 300 micrograms 6-OHDA significant increases in B-wave amplitudes and decreases in retinal DA, DOPAC and HVA concentrations were obtained. This latter dose did not affect retinal concentrations of serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA) and norepinephrine (NE). These results demonstrate that selective reductions of retinal dopamine and its metabolites can be obtained with a single intravitreal injection of 300 micrograms 6-OHDA in rabbits. The observed concomitant increase in B-wave amplitudes lends support to the hypothesis that DA acts as a mediator of lateral inhibition in the retina.     

Effect of chronic nicotine administration on monoamine and monoamine metabolite concentrations in rat brain

The effects on rat brain tissue monoamine and monoamine metabolite concentrations of chronic nicotine administration at two doses (3 and 12 mg/kg/day) using constant infusion were studied. After 21 days of treatment, tissue concentrations of dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT), and several metabolites in striatum, hypothalamus, and frontal cortex were determined by high performance liquid chromatography with electrochemical detection. Compared with a control group, nicotine treatment significantly decreased NE in frontal cortex but not in other regions. The concentration of 5HT also was decreased in frontal cortex but increased in the hypothalamus at the higher dose of nicotine. The 5HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) was not significantly altered in any region. The 5HT index (5-HIAA/5-HT) was significantly decreased in the hypothalamus and increased in frontal cortex at the higher dose. Concentrations of DA and the metabolite homovanillic acid (HVA) were not significantly altered by nicotine. Nevertheless, significant decreases in the DA metabolite dihydroxyphenyl-acetic acid (DOPAC) were observed in both striatum and hypothalamus. Moreover, the DA index [(DOPAC + HVA)/DA] was significantly decreased in all three brain regions. In contrast to other studies using acute dose and in vitro perfusion paradigms that have reported increased CNS catecholamine release stimulated by nicotine, chronic administration appears to be associated with decreased catecholamine turnover in some brain regions.     

Pineal melatonin and brain transmitter monoamines in CBA mice during chronic oral nicotine administration

The effects of chronic oral nicotine administration on the pineal melatonin and brain transmitter monoamines were studied in male CBA mice, which possess a clear daily rhythm of melatonin secretion. On the 50th day of nicotine administration, pineal melatonin as well as cerebral dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), norepinephrine (NE), 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were determined at various times. The chronic nicotine treatment did not alter the timing of the pineal melatonin peak, which occurred at 10 h after the light offset. However, in mice drinking nicotine solution, the nocturnal pineal melatonin levels were lower than in control mice drinking tap water. The chronic nicotine treatment increased the striatal DA, DOPAC, HVA and 5-HIAA levels, the hypothalamic NE, MHPG and 5-HIAA and the cortical MHPG. Most prominent effects of nicotine were found at 8 h after the light offset, when the striatal levels of DA and HVA, hypothalamic NE and MHPG as well as cortical MHPG were significantly elevated in the nicotine-treated mice compared with the control mice. No direct correlation between nicotine's effects on brain transmitter monoamines and on pineal melatonin levels was apparent. The results suggest that chronic nicotine treatment slightly suppresses the melatonin production but does not alter the daily rhythm of pineal melatonin in mice maintained on a light-dark cycle. However, the results indicate that nicotinic receptors might be involved in the regulation of pineal function.     

Methylmercury-induced movement and postural disorders in developing rat: regional analysis of brain catecholamines and indoleamines

Subcutaneous administration of methylmercury (MeHg) to rats during early postnatal development resulted in movement and postural disorders by day 22-24. Tissue concentrations of norepinephrine (NE), serotonin (5-HT), dopamine (DA) and selected metabolites were measured in the cerebral cortex, spinal cord and caudate-putamen at the onset of neurological impairment and at two subclinical stages of toxicity. In the cerebral cortex there was a significant increase in tissue concentrations of 5-HT (54-81%) and 5-hydroxyindoleacetic acid (HIAA, 133-178%) at the onset of neurological impairment. Similar increases were detected in the spinal cord for 5-HT (19-43%) and HIAA (98-123%) as well as an increase in the concentration of NE (42-51%). In the caudate-putamen there were significant increases in the concentrations of NE (98-116%), HIAA (108-124%) and DA (28-29%) with a significant decrease in the concentration of 3,4-dihydroxyphenylacetic acid (DOPAC, 20-27%); however, tissue levels of homovanillic acid (HVA) did not change significantly. Many of these changes were detected at subclinical stages of MeHg toxicity. The ratio of HIAA/5-HT, which is frequently used as an estimate of turnover for 5-HT, was significantly increased in all 3 tissues at the onset of neurological impairment (38-94%) and at one subclinical stage (47-114%). The ratio of (DOPAC + HVA)/DA was significantly decreased in caudate-putamen at all 3 stages of toxicity (18-40%). These changes indicate altered metabolism in aromatic amine systems in the developing central nervous system during the pathogenesis of MeHg-induced movement and postural disorder.     

巴曲酶对脑缺血再灌注细胞外液单胺类及其代谢产物的影响——微透析研究

目的巴曲酶对脑缺血再灌流损伤的保护机理。方法采用脑内微透析技术结合高灵敏度的高压液相色谱－电化学检测手段（ＨＰＬＣ－ＥＤ），测定前脑缺血３０ｍｉｎ再灌注１２０ｍｉｎ时的纹状体细胞外液（ＥＣＦ）的ＤＡ、５－ＨＴ和ＮＥ及其代谢产物（５－ＨＩＡＡ）和ＨＶＡ的变化和巴曲酶的影响。结果显示脑缺血时，ＥＣＦＤＡ、ＮＥ及５－ＨＴ明显升高，巴曲酶能显著地降低脑缺血时ＥＣＦＤＡ及再灌注时ＥＣＦＨＶＡ和５－ＨＩＡＡ的水平。结论巴曲酶影响单胺神经递质是对脑缺血再灌注损伤起保护作用的机理之一     

The effects of hypoxia on catecholamine dynamics in the rat carotid body

The catecholamine content of the rat carotid body was assayed using high performance liquid chromatography with electrochemical detection. The concentration of dopamine (DA) was found to predominate over that of norepinephrine (NE) by a small margin (31 pmol/carotid body pair DA; 23 pmol/carotid body pair NE). The turnover rates of carotid body DA and NE were determined from the time-dependent decline in their concentrations following the blockade of synthesis with alpha-methyl-p-tyrosine. Values were obtained (DA t 1/2 = 1.9 h; NE t 1/2 = 2.3 h) which suggested a rapid turnover of carotid body catecholamines. Exposure of rats to conditions of severe hypoxia (5% O2-95% N2) failed to significantly alter either the content or turnover of carotid body catecholamines. By contrast, the concentration of carotid body DOPAC, a reflection of DA utilization, was significantly elevated following hypoxic conditions. Further, in vivo tyrosine hydroxylase activity was assessed by measuring the accumulation of carotid body DOPA after inhibiting L-aromatic amino acid decarboxylase with NSD-1015. Basal tyrosine hydroxylase activity (approximately 14-16 pmol/carotid body pair/h) also was significantly increased by acute hypoxic exposure. These results, in part, suggest that rat carotid body DA may act as a neurotransmitter whose synthesis and release are coupled to stimulus demand.     

Role of Nitric Oxide in Modulating the Release of Dopamine, Glutamate, and GABA in Striatum of the Freely Moving Rat

This study investigated the role of nitric oxide (NO) in modulating the basal and N-methyl-

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-aspartate (NMDA)-induced release of dopamine (DA), glutamate (GLU), and γ-aminobutiric acid (GABA) in striatum of the freely moving rat using microdialysis. Intrastriatal infusion of NMDA (5 mM) for 15 min increased extracellular concentrations of DA, GLU, and GABA. NMDA also decreased extracellular concentrations of DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC), and 4-hydroxy-3-methoxyphenylacetic acid (HVA), and of the GLU and GABA precursor, glutamine (GLN). Perfusion of N-nitroarginine (1–5 mM), an inhibitor of the synthesis of NO, potentiated NMDA-induced increases in extracellular concentrations of DA and attenuated increases of extracellular GLU. NMDA-induced decreases of extracellular concentrations of DOPAC were also attenuated by N-nitroarginine. N-nitroarginine had no effect on NMDA-induced changes of extracellular concentrations of GABA, HVA, and GLN. N-nitroarginine decreased basal concentrations of DOPAC and HVA, and increase basal concentrations of GLN, but had no effect on basal DA, GLU, and GABA. These results suggest a role for NO in modulating the NMDA-induced release of DA and GLU in striatum. They also suggest that NO could be regulating the basal metabolism of DA, GLU, and GABA.     

Effect of naloxone on morphine-induced changes in striatal dopamine metabolism and glutamate, ascorbic acid and uric acid release in freely moving rats

Recent findings have shown that systemic morphine increases extracellular dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), ascorbic acid (AA) and uric acid concentrations in the striatum of freely moving rats. The morphine-induced increase in DA oxidative metabolism is highly correlated with that of xanthine. In the present study, we evaluated the effects of subcutaneous (s.c.) naloxone (1 mg/kg) on morphine-induced changes in DA, DOPAC, HVA, 5-hydroxyindoleacetic acid (5-HIAA), AA, uric acid and glutamate in the striatum of freely moving rats using microdialysis. Dialysates were assayed by high performance liquid chromatography with electrochemical detection or (glutamate) ultraviolet detection. Morphine (5–20 mg/kg) given s.c. increased DA, DOPAC+HVA, 5-HIAA, AA and uric acid and decreased glutamate dialysate concentrations over a 3 h period after morphine. Morphine (1 mM), given intrastriatally, did not affect all the above parameters, with the exception of an early short-lasting decrease in AA concentration. Naloxone antagonised all morphine-induced changes with the exception of AA increase and glutamate decrease in dialysate concentrations. Systemic or intrastrial (0.2–2 mM) naloxone increased AA and decreased glutamate dialysate concentrations. When given intranigrally, morphine (1 mM) increased DOPAC+HVA, AA and uric acid and decreased glutamate dialysate concentrations over a 2 h period after morphine; DA and 5-HIAA concentrations were unaffected. These results suggest that: (i) morphine increases striatal DA release and 5-hydroxytryptamine oxidative metabolism by a μ-opioid receptor-mediated mechanism mainly at extranigrostriatal sites; (ii) morphine increases DA and xanthine oxidative metabolism and affects glutamate and AA release by a μ-opioid receptor mediated mechanism acting also at nigral sites; and (iii) a μ-opioid receptor-mediated mechanism tonically controls at striatal sites extracellular AA and glutamate concentrations.