Simple,rapid procedure for the determination of valproate and ethosuximide in plasma by gas—liquid chromatography

A simple method based on high-performance liquid column chromatography with electrochemical detection is described for the simultaneous determination of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in discrete brain regions of rats. The supernatant of a tissue homogenate is injected directly onto a liquid chromatograph, thus omitting the commonly adopted adsorption step. Of the four different supports tested Nucleosil C₁₉ (5 μm) was found superior with respect to chromatographic performance. The effects of pH, methanol and the ion-pairing agent hexyl sulfate on the retention were studied. The mobile phase used in the final studies consisted of citrate buffer pH 4.25—methanol (92:8, v/v) containing hexyl sulfate (1.7 · 10^?3M). Standard curves of dopamine, DOPAC and HVA were found linear up to about 600 pmol per injection for each compound. The precisions of the chromatographic step were (s_rel. %): 0.72% (dopamine), 1.26% (DOPAC) and 2.69% (HVA).     

Determination of dopamine, homovanillic acid and 3,4-dihydroxyphenylacetic acid in rat brain striatum by high-performance liquid chromatography with electrochemical detection

Two procedures using liquid chromatography with electrochemical detection are described for the determination of dopamine (DA) and its two acidic metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), in subregions of rat striatum and nucleus accumbens. A strong cation-exchange column was used for DA analysis and a C₁ reversed-phase column was used for the analysis of the metabolites. Effects of pH, temperature and percentage of methanol on the retention time of HVA and DOPAC were studied. Levels of these compounds in the subregions of rat striatum and nucleus accumbens are reported.     

Relationship of extracellular dopamine in striatum of newborn piglets to cortical oxygen pressure

The present studies describes the relationship between extracellular dopamine in striatum of newborn piglets and cortical oxygen pressure. The extracellular level of dopamine was measured by in vivo microdialysis and the oxygen pressure in the cortex was measured by phosphorescence lifetime of oxygen probe in the blood. Controlled, graded levels of hypoxic insult to the brain of animals were generated by decreasing of the oxygen fraction in the inspired gas (FiO₂) from 21% to 14%, 11%, and 9%. This resulted in decrease in the cortical oxygen pressure from 31–35 Torr to about 24 Torr, 15 Torr and 4 Torr, respectively. The changes in extracellular level of dopamine, DOPAC and HVA were dependent on changes in cortical oxygen pressure. Stepwise decrease in the cortical oxygen pressure (see above) caused increases in extracellular dopamine of about 80%, 200% and 550%, respectively. The levels of DOPAC and HVA progressively decreased and when cortical oxygen decreased to 4–6 Torr were about 50% and 70% of control. respectively. After return of FiO₂ to control (21%), the cortical oxygen pressure rapidly increased to above normal, then returned to control values. The extracellular levels of dopamine, DOPAC, and HVA recovered more slowly, attaining control values in about 30 minutes. The data show that extracellular levels of dopamine increase with even very small decreases in oxygen pressure. Thus, there is no oxygen reserve which protects dopamine release and metabolism from decrease in oxygen pressure.     

Fully automated high-performance liquid chromatography of ciprofloxacin with direct injection of plasma and Mueller–Hinton broth for pharmacokinetic/pharmacodynamic studies

An isocratic high-performance liquid chromatographic method with column switching and direct injection has been developed to determine ciprofloxacin in plasma and Mueller–Hinton broth. An on-line dilution of the sample was performed with a loading mobile phase consisting of 173 mM phosphoric acid. The analyte was retained on a LiChrocart 4-4 precolumn filled with a LiChrospher 100 RP18, 5 μm. An electric-actuated system with two six-port valves allowed a clean-up step with a mixture 20 mM phosphate buffer (pH 3.5)–methanol (97: 3, v/v) and the transfer of the analyte by a back-flush mode to a 150×4.6 mm I.D. column packed with a Kromasil C₈ 5 μm, using a mobile phase of 20 mM phosphate buffer (pH 3.5)–acetonitrile (85:15, v/v). Fluorescence detection allowed a quantification limit of 0.078 μg/ml with a 40-μl sample size. The method was evaluated to determine its usefulness in studying the pharmacokinetic/pharmacodynamic behaviour of ciprofloxacin in an in vitro model.     

Effects of Manganese on Extracellular Levels of Dopamine in Rat Striatum: An Analysis <Emphasis Type="Italic">In vivo</Emphasis> by Brain Microdialysis

The aim of this study is to determine the effects of intrastriatal administration of MnCl_2, on the extracellular levels of dopamine (DA) and metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in basal conditions and stimulated by depolarization with KCl and pargyline administration. Also, we studied the effect of MnCl₂ on extracellular levels of l-Dopa in the presence of aromatic amino acid decarboxylase (AADC) inhibitor 3-hydroxybencilhydracine-HCl (NSD 1015). This study concluded that MnCl₂, reduced the basal and K⁺-stimulated DA-release in striatum, without notably affecting the DOPAC and HVA levels. Intraperitoneal injection of pargyline increased striatal DA levels, decreasing DOPAC and HVA levels. The infusion of MnCl₂ removed the increase in DA levels, without affecting DOPAC and HVA levels. Perfusion of NSD 1015 increased the extracellular levels of l-DOPA in striatum, and MnCl₂ increased the effect of NSD1015 on l-Dopa.     

The use of C8-octyl columns for the analysis of catecholamines by ion-pair reversed-phase liquid chromatography with amperometric detection

The chromatographic behavior of norepinephrine (NE), epinephrine, dopamine, 3,4-dihydroxyphenylalanine, and 3,4-dihydroxyphenylacetic acid on octylsilane (C₈) reversed-phase high-performance liquid chromatography columns was observed under various mobile phase conditions including manipulations of pH, pairing ion and methanol concentrations. The optimum isocratic conditions permitting quantitative resolution of these substances in minimum time and with maximum detector response were determined. Employing a pH 3.0–3.2 mobile phase comprising an aqueous buffer solution containing 0.1 M NaH₂PO₄, 0.1 mM EDTA, and 0.2 mM 1-octanesulfonate, admixed with a volume of methanol equal to 4% of the aqueous volume, the performance of the C₈ columns compares favorably to that of the more widely used C₁₈ columns. The column eluates were monitored with an amperometric detector utilizing a glassy-carbon flow-cell electrode. The detector response for NE was 1.5–2.0 nA/ng and the baseline noise was as little as 0.002 nA thereby permitting quantitation of 5-pg levels or more in the injected samples. By coupling the liquid chromatographic system to a procedure which eliminates non-catechol contaminants from the neuronal and body fluid specimens by alumina adsorption of the catechols, a sensitive and dependable method was developed and employed for the determination of catechol levels in discrete regions of rat brain, cat spinal cord, and in human plasma.     

Determination of monoamine oxidase B activity by high-performance liquid chromatography with electrochemical detection

A sensitive high-performance liquid chromatography method with electrochemical detection for measuring monoamine oxidase B activity in blood platelets is described. Dopamine is used as substrate and is incubated with isolated platelets and aldehyde dehydrogenase to convert dihydroxyphenylacetaldehyde to dihydroxyphenylacetic acid (DOPAC). The acid and the added internal standard hydrocaffeic acid are separated from dopamine and the incubation mixture by extraction with 5 ml of ethyl acetate-toluene (5:1, v/v). The organic phase is evaporated under nitrogen stream and the residue dissolved in 0.1 M critic acid. Dihydroxyphenylacetic acid and the internal standard dihydrocaffeic acid are then separated on the Eurosphere 100-C₁₈ 5 μm column. The mobile phase used was a mixture of sodium acetate, citric acid, and acetonitrile at pH 2.5. The standard curve was linear from 125 pg to 10 ng. Absolute recovery of DOPAC was 85±3.8% and of hydrocaffeic acid 87±4.1%. The method presented is sensitive (detection limit 8.0 pg of DOPAC injected) and reproducible (coefficient of variation 0.4-1%) with good accuracy (94–98%).     

In Vivo Measurement of Dopamine and Its Metabolites by Intracerebral Dialysis: Changes After d-Amphetamine

Abstract: By using a new technique, intracerebral dialysis, in combination with high performance liquid chromatography and electrochemical detection, it was possible to recover and measure endogenous extracellular dopamine, together with its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) from the striatum and nucleus accumbens of anaesthetized or freely moving rats. In addition, measurements of extracellular 5-hydroxyindoleacetic acid, ascorbic acid, and uric acid were made. Basal extracellular concentrations of dopamine and DOPAC in the striatum were estimated to be 5 × 10⁻⁸ M and 5 × 10⁻⁶ M , respectively. d -Amphetamine (2 mg/kg s.c.) increased dopamine levels in the striatum perfusates by 14-fold, whereas levels of DOPAC and HVA decreased by 77% and 66%, respectively.     

Determination of fenofibric acid in human plasma using automated solid-phase extraction coupled to liquid chromatography

The pharmacokinetic studies of fenofibrate require a rapid, selective and robust method to allow the determination of fenofibric acid, its active metabolite, in different biological matrixes (such as plasma, serum or urine). A new fully automated method for the determination of fenofibric acid in plasma has been developed, which involves the solid-phase extraction (SPE) of the analyte from plasma on disposable extraction cartridges (DECs) and reversed-phase HPLC with UV detection. The SPE operations were performed automatically by means of a sample processor equipped with a robotic arm (ASPEC system). The DEC filled with octadecyl silica was first conditioned with methanol and pH 7.4 phosphate buffer. A 0.8-ml volume of diluted plasma sample containing the internal standard (sulindac) was then applied on the DEC. The washing step was performed with the same buffer (pH 7.4). Finally, the analytes were successively eluted with methanol (1.0 ml) and 0.04 M phosphoric acid (1.0 ml). After a mixing step, 100 μl of the resultant extract was directly introduced into the HPLC system. The liquid chromatographic (LC) separation of the analytes was achieved on a Nucleosil RP-8 stationary phase (5 μm). The mobile phase consisted of a mixture of methanol and 0.04 M phosphoric acid (60:40, v/v). The analyte was monitored photometrically at 288 nm. The method developed was validated. In these conditions, the absolute recovery of fenofibric acid was close to 100% and a linear calibration curve was obtained in the concentration range from 0.25 to 20 μg/ml. The mean RSD values for repeatability and intermediate precision were 1.7 and 3.9% for fenofibric acid. The method developed was successfully used to investigate the bioequivalence between a micronized fenofibrate capsule formulation and a fenofibrate Lidose™ formulation.     

Determination of zolpidem in serum microsamples by high-performance liquid chromatography and its application to pharmacokinetics in rats

A single-solvent extraction step high-performance liquid chromatographic method is described for quantitating zolpidem in rat serum microsamples (50 μl). The separation used a 2.1 mm I.D. reversed-phase OD-5-100 C₁₈ column, 5 μm particle size with an isocratic mobile phase consisting of methanol–acetonitrile–26 mM sodium acetate buffer (adjusted to pH 2.0 with 40% phosphoric acid) containing 0.26 mM tetrabutylammonium phosphate (13:10:77, v/v/v). The detection limit was 3 ng/ml for zolpidem using an ultraviolet detector operated at 240 nm. The recovery was greater than 87% with analysis performed in 12 min. The method is simple, rapid, and applicable to pharmacokinetic studies of zolpidem after administering two intravenous bolus doses (1 and 4 mg/kg) in rats.     

Effects of Apomorphine on In Vivo Release of Dopamine and Its Metabolites in the Prefrontal Cortex and the Striatum, Studied by a Microdialysis Method

The effects of apomorphine (0.1-2.5 mg/kg) on release of endogenous dopamine and extracellular levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the prefrontal cortex and the striatum were examined in vivo by a microdialysis method. Apomorphine significantly reduced release of dopamine and the extracellular levels of dopamine metabolites, DOPAC and HVA, not only in the striatum, but also in the prefrontal cortex. These findings indicate that dopamine autoreceptors modulate in vivo release of dopamine in the prefrontal cortex.     

Effect of Hemorrhagic Hypotension on Cortical Oxygen Pressure and Striatal Extracellular Dopamine in Cat Brain

This study investigated the relationships between blood pressure, cortical oxygen pressure, and extracellular striatal dopamine in the brain of adult cats during hemorrhagic hypotension and re-transfusion. Oxygen pressure in the blood of the cortex was measured by the oxygen dependent quenching of phosphorescence and extracellular dopamine, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) by in vivo microdialysis. Following a 2 h stabilization period after implantation of the microdialysis probe in the striatum, the mean arterial blood pressure (MAP) was decreased in a stepwise manner from 132 ± 2 Torr (control) to 90 Torr, 70 Torr and 50 Torr, holding the pressure at each level for 15 min. The whole blood was then retransfused and measurements were continued for 90 min. As the MAP was lowered there was a decrease in arterial pH, from a control value of 7.37 ± 0.05 to 7.26 ± 0.06. The PaCO₂ decreased during bleeding from 32.3 ± 4.8 Torr to 19.6 ± 3.6 Torr and returned to 30.9 ± 3.9 Torr after retransfusion. The PaO₂ was 125.9 ± 15 Torr during control conditions and did not significantly change during bleeding. Cortical oxygen pressure decreased with decrease in MAP, from 50 ± 2 Torr (control) to 42 ± 1 Torr, 31 ± 2 Torr and 22 ± 2 Torr, respectively. A statistically significant increase in striatal extracellular dopamine, to 2,580 ± 714% of control was observed when MAP decreased to below 70 Torr and cortical oxygen pressure decreased to below 31 Torr. When the MAP reached 50 Torr, the concentration of extracellular dopamine increased to 18,359 ± 2,764% of the control value. A statistically significant decrease in DOPAC and HVA were observed during the last step of bleeding. The data show that decreases in systemic blood pressure result in decrease in oxygen pressure in the microvasculature of the cortex, suggesting vascular dilation is not sufficient to result in a full compensation for the decreased MAP. The decrease in cortical oxygen pressure to below 32 Torr is accompanied by a marked increase in extracellular dopamine in the striatum, indicating that even such mild hypoxia can induce significant disturbance in brain metabolism.     

High-performance liquid chromatographic assay with fluorescence detection for the determination of cephaeline and emetine in human plasma and urine

A high-performance liquid chromatographic assay method for the quantitation of ipecac alkaloids (cephaeline and emetine) in human plasma and urine is described. Human plasma or urine was extracted with diethylether under alkaline conditions following the addition of an internal standard. Concentrations of alkaloids and internal standard were determined by octadecylsilica chromatographic separation (Symmetry C₁₈ columns, plasma analysis; 15 cm×4.6 mm I.D., 5 μm particle size, urine analysis; 7.5 cm×4.6 mm I.D., 5 μm particle size). The mobile phase consisted of buffer (20 mmol/l 1-heptanesulfonic acid sodium salt, adjusted to pH 4.0 with acetic acid)–methanol (51:49, v/v). Eluate fluorescence was monitored at 285/316 nm. The lowest quantitation limits of cephaeline and emetine were 1 and 2.5 ng/ml, respectively, in plasma, and 5 ng/ml in urine. Intra- and inter-day relative standard deviations were below 15%. The assay is sensitive, specific and applicable to pharmacokinetic studies in humans.     

Study of Dopamine Turnover by Monitoring the Decline of Dopamine Metabolites in Rat CSF After α-Methyl-p-Tyrosine

CSF was continuously withdrawn from the third ventricle of anesthetized rats. CSF 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid concentrations were determined every 15 min by liquid chromatography coupled with electrochemical detection. Acute tyrosine hydroxylase inhibition [with alpha-methyl-p-tyrosine (alpha-MPT)] induced an exponential decline in levels of DOPAC and HVA in CSF. The decline in DOPAC and HVA concentrations was identical in CSF and forebrain but was much slower in the striatum, suggesting that CSF metabolites of 3,4-dihydroxyphenylethylamine (dopamine) reflect whole forebrain metabolites. The decay in CSF DOPAC and HVA levels after dopamine synthesis inhibition was also used as an in vivo index of forebrain dopamine turnover after various pharmacological treatments. Haloperidol pretreatment accelerated this decay, confirming the increase in brain dopamine turnover induced by neuroleptics. After reserpine pretreatment (15 h before), alpha-MPT produced a very sharp decay in levels of DOPAC and HVA. This result indicates that the residual dopamine that cannot be stored after reserpine treatment is very rapidly renewed and metabolized. Nomifensine strongly diminished the slope of DOPAC and HVA level decreases after alpha-MPT, a result which can be explained either by a slower dopamine turnover or by the involvement of storage dopamine pools. These results exemplify the use of monitoring the decay of dopamine metabolites after alpha-MPT administration in the study of the pharmacological action of drugs on the central nervous system of the rat.     

Rapid and simple method for the determination of urinary benzoic and phenylacetic acids and their glycine conjugates in ruminants by reversed-phase high-performance liquid chromatography

A simple, rapid and reproducible reversed-phase high-performance liquid chromatographic method for the simultaneous determination of benzoic acid (BA), phenylacetic acid (PAA) and their respective glycine conjugates hippuric acid (HA) and phenaceturic acid (PA) in sheep urine is described. The procedure involves only direct injection of a diluted urine sample, thus obviating the need for an extraction step or an internal standard. The compounds were separated on a Nova-Pak C₁₈ column with isocratic elution with acetate buffer (25 mM, pH 4.5)—methanol (95:5). A flow-rate of 1.0 ml/min, a column temperature of 35°C and detection at 230 nm were employed. These conditions were optimized by investigating the effects of pH, molarity, methanol concentration in the mobile phase and column temperature on the resolution of the metabolites. The total analysis time was less than 15 min per sample. At a signal-to-noise ratio of 3 the detection limits for ten-fold diluted urine were 1.0 μg/ml for BA and HA and 5.0 μg/ml for PAA and PA with a 20-μl injection.     

Simultaneous determination of phenylbutazone and its metabolites in plasma and urine by high-performance liquid chromatography

A high-performance liquid chromatographic method was developed for the simultaneous determination of phenylbutazone and its metabolites, oxyphenbutazone and γ-hydroxyphenylbutazone, in plasma and urine. Samples were acidified with hydrochloric acid and extracted with benzene—cyclohexane (1:1, v/v). The extract was redissolved in methanol and chromatographed on a μBondapak C₁₅ column using a mobile phase of methanol—0.01 M sodium acetate buffer (pH 4.0) in a linear gradient (50 to 100% methanol at 5%/min; flow-rate 2.0 ml/min) in a high-performance liquid chromatograph equipped with an ultra-violet absorbance detector (254 nm). The detection limit for phenylbutazone, oxyphenbutazone and for γ-hydroxyphenylbutazone was 0.05 μg/ml.A precise and sensitive assay for the determination of phenylbutazone and its metabolites was established.     

Relationships of Dopamine, Cortical Oxygen Pressure, and Hydroxyl Radicals in Brain of Newborn Piglets During Hypoxia and Posthypoxic Recovery

Abstract: The present study describes the relationships of extracellular striatal dopamine, cortical oxygen pressure, and striatal hydroxyl radicals in brain of newborn piglets during hypoxia and posthypoxic reoxygenation. Hypoxia was induced by reducing the fraction of inspired oxygen (F_iO₂) from 22% (control) to 7% for 1 h. The F_iO₂ was then returned to the control value and measurements were continued for 2 h. Cerebral oxygen pressure was measured by the oxygen dependent quenching of phosphorescence and extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and hydroxy radicals in the striatum were determined by in vivo microdialysis. Hypoxia decreased the cortical oxygen pressure from 47 ± 2 to 9 ± 1.3 torr (p < 0.001); the levels of extracellular dopamine in the striatum increased to 16,000 ± 3,270% of control (p < 0.01), whereas the levels of DOPAC and HVA decreased to 25.3 ± 6% (p < 0.001) and 36 ± 5% (p < 0.01) of control, respectively. Compared with control, the hydroxyl radical levels at each time point were not significantly increased during hypoxia, although the sum of the measured values was significantly increased (p < 0.05). During the first 5 min after F_iO₂ was returned to 22%, the cortical oxygen pressure increased to control values and stayed at this level for the remainder of the measurement period. The extracellular level of dopamine declined to values not statistically different from control during 40 min of reoxygenation. During the first 10 min of reoxygenation, DOPAC and HVA further decreased and then began to slowly increase. By 70 min of reoxygenation, the values were not significantly different from control. Hydroxyl radicals were above control during the entire period of reoxygenation, with maximal values observed after 100 min of reoxygenation. This increase was largely abolished by injecting the animals with α-methyl-p-tyrosine 5 h before hypoxia, a procedure that depleted the brain of dopamine. Our results suggest that oxidation of striatal dopamine during posthypoxic reoxygenation is at least partly responsible for the observed increase in striatal level of hydroxyl radicals that may exacerbate posthypoxic cerebral injury.     

Role of Monoamine Oxidase Type A and B on the Dopamine Metabolism in Discrete Regions of the Primate Brain

The role of monoamine oxidase (MAO) type A and B on the metabolism of dopamine (DA) in discrete regions of the monkey brain was studied. Monkeys were administered (–)-deprenyl (0.25 mg/kg) or clorgyline (1.0 mg/kg) or deprenyl and clorgyline together by intramuscular injections for 8 days. Levels of DA and its metabolites, dihydroxy phenylacetic acid (DOPAC) and homovanillic acid (HVA) were estimated in frontal cortex (FC), motor cortex (MC), occipital cortex (OC), entorhinal cortex (EC), hippocampus (HI), hypothalamus (HY), caudate nucleus (CN), globus pallidus (GP) and substantia nigra (SN). (–)-Deprenyl administration significantly increased DA levels in FC, HY, CN, GP and SN (39–87%). This was accompanied by a reduction in the levels of DOPAC (37–66%) and HVA (27–79%). Clorgyline administration resulted in MAO-A inhibition by more than 87% but failed to increase DA levels in any of the brain regions studied. Combined treatment of (–)-deprenyl and clorgyline inhibited both types of MAO by more than 90% and DA levels were increased (57–245%) in all brain regions studied with a corresponding decrease in the DOPAC (49–83%) and HVA (54–88%) levels. Our results suggest that DA is metabolized preferentially, if not exclusively by MAO-B in some regions of the monkey brain.     

Endogenous homovanillic acid levels differ between rat and rabbit caudate,hippocampus, and cortical regions

Endogenous dopamine (DA) levels and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3MT) and homovanillic acid (HVA) were measured by high-performance liquid chromatography in the entorhinal-piriform (EnPi), cingulate (CIN), sensorimotor (SSM) and visual (VIS) cortices as well as is the caudate (CAU) and hippocampus (HIP) of Sprague-Dawley (SD) rats and New Zealand (NZ) rabbits. The DA, DOPAC and 3MT contents were similar in both species. The HVA levels however, although they followed DA distribution, were several-fold higher in NZ rabbits than in SD rats for all cortices, HIP and CAU. In addition, total metabolite contents and DA turnove (estimated from DA metabolite/DA ratios) were significantly higher in NZ rabbits than in SD rats, suggesting an increased release and/or metabolism in the former species. The HVA/DA ratios were much higher for NZ rabbit regions than for SD rats, indicating an increased DA release in the former species since the DOPAC/DA ratios (index of intraneuronal degradation) were similar.Herbert H. Jasper Postdoctoral Fellow, Centre de recherche en sciences neurologiques.     

Effects of an N-methyl-d-aspartate receptor agonist and its antagonist CPP on the levels of dopamine and serotonin metabolites in rat striatum collected in vivo by using a brain dialysis technique

3-((±)-2-Carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) is an antagonist at the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. In the present study, levels of dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA) were measured after intracerebroventricular injection of NMDA, CPP or both in rat striatum using a brain dialysis method. The injection of NMDA produced a significant increase in DOPAC level. HVA level was also increased by NMDA injection. The level of 5-HIAA was not affected by NMDA injection. The injection of CPP had no effect on DOPAC, HVA and 5-HIAA levels. The injection of CPP restrained the increase of DOPAC and HVA levels induced by NMDA injection. The results suggest that intracerebral injection of NMDA may increase dopamine release from rat striatum, but have no effect on serotonin release. Furthermore, CPP inhibits NMDA induced release of dopamine.