Accumulation and disappearance of noradrenaline and its major metabolites synthesized from intraventricularly injected (3H)dopamine in the rat brain

Broccoli-shaped biosensor hierarchy for electrochemical screening of noradrenaline in living cells

Monitoring and determination of ultra-trace concentrations of monoamine neurotransmitter such as noradrenaline (NA) in living cells with simple, sensitive and selective assays are significantly interesting. We design NA-electrode sensing system based on C-, N-doped NiO broccoli-like hierarchy (CNNB). The spherical broccoli-head umbrella architectures associated with nano-tubular arrangements enabled to tailor NA biosensor design. The homogenous doping and anisotropic dispersion of CN nanospheres along the entire NB head nanotubes lead to creating of abundant electroactive sites in the interior tubular vessels and outer surfaces for ultrasensitive detection of NA in living cells such as PC12. The CNNB biosensor electrodes showed efficient electrocatalytic activity, enhanced kinetics for electrooxidation of NA, and fast electron-transfer between electrode-electrolyte interface surfaces, enabling synergistic enhancement in sensitivity, and selectivity at a low-detectable concentration of ∼ 6nM and reproducibility of broccoli-shaped NA-electrodes. The integrated CNNB biosensor electrodes showed evidence of monitoring and screening of NA released from PC12 cells under K⁺ ion-extracellular stimulation process. The unique features of CNNB in terms of NA-selectivity among multi-competitive components, long-term stability during the detection of NA may open their practical, in-vitro application for extracellular monoamine neurotransmitters detection in living cells.

Determination of ultra-trace catecholamines based on hot electron-induced cathodic electrochemiluminescence at a naturally oxide-covered tantalum electrode

A naturally oxide-covered tantalum electrode is firstly used in the detection of ultra-trace catecholamines based on hot electron-induced cathodic electrochemiluminescence with extremely low background, excellent sensitivity and perfect stability.

Catecholamines and methods for their identification and quantitation in biological tissues and fluids

Catecholamines act via dopaminergic-, and adrenergic receptors, and are involved in a variety of regulatory systems. They take part in regulation of the response to stress, psychomotor activity, emotional processes, learning, sleep and memory. Due to many catecholaminergic pathways, and a wide range of functions they are involved in, both in the central nervous system and in periphery, a development of the reliable techniques for their extraction and quantitation is essential. This paper presents an overview of the currently applied methodologies for catecholamines detection and identification in various biological samples.

Determination of 3,4-dihydroxyphenyl glycol in plasma by gas chromatography-mass spectrometry and high-performance liquid chromatography methods

Several modifications of GC-MS and HPLC methods for plasma level DHPG have been described. The effects of storage temperature and stabilizing agents on DHPG stability have been studied. The stabilizing agent has been found to play a more important role than low-temperature storage in preventing DHPG from decomposition during sample storage. A specific and sensitive GC-MS method (electron impact) has been established using stable isotope-labeled DHPG as an internal standard. HPLC has been improved by modifying the conditions, resulting in a good separation of DHPG and internal standard from solvent front other early eluting compounds. Comparison of the GC-MS and HPLC procedures demonstrates a strong correlation between these two methods.

Noradrenaline metabolism in neocortex and hippocampus following transient forebrain ischemia in rats: relation to development of selective neuronal necrosis

Noradrenaline (NA) metabolism in the neocortex and hippocampus was examined in rats at 1, 24, and 48 h following 15 min of reversible forebrain ischemia. As assessed by the ratio of accumulated 3,4-dihydroxyphenylalanine (DOPA) to the tissue NA level after inhibition of DOPA decarboxylase, the NA turnover rates were markedly increased (120-148% above the control) at 1 h postischemia in both the neocortex and hippocampal formation (CA1 and CA3 plus dentate gyrus). The DOPA:NA ratio went back to control levels after longer postischemic survival times. The ratio between levels of the deaminated NA metabolite, 3,4-dihydroxyphenylethyleneglycol (DOPEG), and NA, which gives another measure of NA turnover rate, showed similar changes. In the neocortex and the CA3 plus dentate gyrus, the DOPEG:NA ratio was markedly increased (89-118%) 1 h after the ischemia, but this change had disappeared at 24 and 48 h. Thus, both the DOPA accumulation experiments and the NA and DOPEG measurements indicate that following transient forebrain ischemia, there is an increased NA turnover in the hippocampus and cortex only in the early recirculation period and not after longer postischemic survival times. The degree of neuronal necrosis in the CA1 region was examined light microscopically on celestine blue-acid fuchsin-stained sections at 24, 48, and 96 h following the ischemic insult. The neuronal damage in CA1 was sparse after 24 h of recovery, had increased markedly after 48 h, and was very pronounced at 96 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of monoamines and monoamine metabolites in various brain regions of six shark species

1. The concentrations of six monoamines or monoamine metabolites were measured in six brain regions of six shark species using high performance liquid chromatography with electrochemical detection. 2. Serotonin concentrations were greatest in the hypothalamus and tegmentum, intermediate in the midline ridge formation, spinal cord and forebrain, and lowest in the cerebellum in all species. 3. Specie differences in dopamien concentration were significant only in the forebrain; species differences in the levels of the norepinephrine, epinephrine and 5-hydroxyindoleacetic acid were significant in most brain regions, including the midline ridge formation. 4. Differences and similarities to the mammalian pattern of monoamine distribution in the brain are discussed.

Kinetics of intraventricularly injected trace amines and their deuterated isotopomers

Intraventricular injection into the rat brain of four trace amines and a catecholamine resulted in rapid exponential loss of the amines in the first 30 minutes after injection. The half-lives were: phenylethylamine 3.8 min, para-tyramine 5.1 min, meta-tyramine 7.4 min and dopamine 8.0 min. Tryptamine showed a biphasic loss with half-lives of 4.7 min (over the 5 to 10 min period) and 14.1 min (10 to 30 min). The half-lives were substantially increased by deuterium labeling at the alpha carbon position: phenylethylamine 4.8 min, para-tyramine 8.8 min, meta-tyramine 14.1 min, dopamine 13.0 min and tryptamine 6.0 min (5 to 10 min period) and 28.7 min (10 to 20 min). The loss of the amines was reduced by monoamine oxidase inhibition by pargyline hydrochloride and the deuterium isotope effect was abolished. It is noteworthy that the half-life of dopamine was similar to those of the trace amines in this time period and that the trace amine half-lives after i.v. injection was longer than those obtained from measurements of increases of concentrations of endogenous amines after MAOI in vivo and that of dopamine shorter than values calculated from turnover measurements.

Unchanged regional norepinephrine glycol metabolite levels in rat brain two months after amygdala kindling

Concentrations of the norepinephrine (NE) glycol metabolites MHPG (3-methoxy-4-hydroxyphenylethyleneglycol) and DHPG (3,4-dihydroxyphenylethyleneglycol) were examined in 13 brain regions of amygdala-kindled and yoked control rats. The subjects were killed 2 months after the kindled rats had exhibited their sixth 'stage 4-5' generalized seizure. In experiment 1, small but statistically significant decreases in total MHPG levels were found in the right hippocampus (91.6% of control) and hypothalamus (90.7% of control). When the study was repeated with 2 additional control groups, non-kindled, electrically stimulated controls and maximal electroshock convulsion controls, however, these small changes were not seen. The data suggest that since amygdala kindling does not produce any consistent, long-lasting alterations in brain regional NE glycol metabolite levels, there are no consistent, long-term changes in central NE neuronal activity.

Distribution of 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylglycol (DOPEG) in microdissected brain structures and the pituitary gland: metabolite changes in the median eminence in response to hyperprolactinemia and suckling

Dopamine (DA), norepinephrine (NE), epinephrine (E), 3,4-dihydroxyphenylglycol (DOPEG) and dihydroxyphenylacetic acid (DOPAC) were determined simultaneously by a radioenzymatic, thin-layer chromatographic assay able to detect 1-10 pg of the parent compounds and 80-120 pg of their metabolites. A localization study of these compounds in 20 micro-dissected hypothalamic and limbic structures and the anterior and posterior pituitary glands of male rats was completed. DOPAC was detectable in 14 of 22 structures with the lowest DOPAC/DA ratio being found in the caudate nucleus (7.1%) and the highest in the medial aspect of the ventromedial nucleus of the hypothalamus (422.0%). There was a higher DOPAC/DA ratio in the lateral (21.5%) than in the medial (11.3%) portion of the median eminence suggesting that a greater portion of released DA in the medial median eminence enters the portal circulation. DOPEG was detectable in 6 of 22 structures with DOPEG/NE ratios ranging from 8% (interstitial nucleus of the stria terminalis, ventral aspect) to 32% (medial median eminence). A poor correlation exists between DOPAC and DA concentrations in the various brain regions while there was a stronger relationship between DOPEG and NE concentrations. Male rats were rendered hyper-prolactinemic for 48 hours with injections of ovine prolactin (oPRL) every 8 hours (4 mg/kg body weight sc). In such rats there was a suppression of endogenous rat PRL (rPRL) secretion, the DOPAC/DA ratio increased 2.2-fold in the medial (MEm) and 1.9-fold in the lateral median eminence (MEl), and the DA concentration in the anterior pituitary also increased 2.6-fold. In 10 day postpartum lactating rats, suckling produced marked increases in serum rPRL but no change in DOPAC/DA ratios in the ME or in the DA concentration in the anterior pituitary. The data reveal a wide range of DOPAC/DA ratios (7-422%) in brain regions containing cell bodies, axons and terminals of the different dopaminergic neuronal tracts in brain and pituitary. Considering the DOPAC/DA ratios in the MEm and MEl, it is suggested that a large perturbation of dopaminergic transmission produces a significant ratio change while a smaller perturbation is not detected by this index of neuronal metabolism.

Is 3,4-dihydroxyphenylglycol the major route of central norepinephrine metabolism in rat brain?

Central norepinephrine (NE) metabolism was assessed by measuring 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3,4-dihydroxyphenylethyleneglycol (DHPG) in different rat brain areas after saline or probenecid (300 mg/kg) administration. Under probenecid, results showed an increased accumulation of total MHPG and DHPG, and a clear preponderance of DHPG levels over MHPG in almost all the brain areas examined. Estimation of their formation rates confirmed that in basal conditions DHPG is formed more rapidly. This study supports the notion that, without ruling out the importance of MHPG, brain DHPG may be a useful index of central NE activity.

Studies on 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG) levels in human urine, plasma and cerebrospinal fluids, and their significance in studies of depression

Both concentrations of total 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG) in the human urine, plasma and CSF were determined with a high-pressure liquid chromatography with electrochemical detection in order to clarify the dynamic change in these noradrenaline metabolites. Three different biological fluids were collected simultaneously from 16 orthopedic patients who were regarded clinically as substitutes for normal subjects. In the urine, the MHPG concentrations were 1.67 +/- 0.65 micrograms/mg creatinine (mean +/- S.D.) and DHPG 0.39 microgram/mg creatinine +/- 0.21. The plasma levels were 21.16 ng/ml +/- 9.58 for MHPG, and 19.58 ng/ml +/- 8.13 for DHPG. The CSF levels of MHPG and DHPG were 24.08 ng/ml +/- 8.10 and 34.76 ng/ml +/- 11.46, respectively. The CSF levels of these metabolites were correlated significantly with those in the plasma (r = 0.852, p less than 0.001 for MHPG; r = 0.799, p less than 0.001 for DHPG), while no significant correlations were found between the urinary levels and either the plasma or CSF levels of these metabolites. In the urine, the MHPG levels were proportional to the DHPG levels, while the former were inversely proportional to the latter in the plasma or CSF. Neither the MHPG nor DHPG levels in the urine from depressed patients revealed to have any significant correlation with their clinical assessments using the Hamilton Rating Scale Score (HRS). The patients were treated with an antidepressant active selectively on the noradrenergic system, and no significant changes in urinary excretion of these metabolites were observed before and after the drug treatment. These findings suggest that in the case of psychiatric disorders such as depression, these compound levels in the plasma or CSF would provide more important information than those in the urine.

Lack of circadian rhythm in plasma levels of 3,4-dihydroxyphenylethyleneglycol in healthy human subjects

In order to investigate the possible existence of a circadian rhythm in plasma free and sulfate-conjugated 3,4-dihydroxyphenylethyleneglycol (DOPEG), the plasma levels of this metabolite (and for comparison, of melatonin and cortisol) were measured in seven healthy volunteers at 4-h intervals over a period of 24 h. Plasma concentrations of melatonin and cortisol showed distinct diurnal variations with acrophases at 2.5 h and 8.5 h, respectively. In contrast, plasma free DOPEG levels were relatively stable over the 24-h period studied. Sulfate-conjugated and free + sulfate-conjugated DOPEG levels showed a slight, non-significant increase in the early afternoon. These results indicate that in contrast to plasma 3-methoxy 4-hydroxyphenylethyleneglycol, plasma free and conjugated DOPEG levels do not exhibit a circadian rhythm.

Liquid chromatographic determination of free and conjugated 3-methoxy-4-hydroxyphenylethylene glycol with wide-ranging substances related to monoamine metabolism

A simple and sensitive procedure was developed for the simultaneous determination of substances metabolically related to monoamine transmitters including 3-methoxy-4-hydroxy-phenylethylene glycol (MOPEG) in dissected brain regions of rats using high-performance liquid chromatography combined with electrochemical detection. The tissue sample was homogenized in HCl solution. The homogenate was divided into two portions, of which one was used for the assay of MOPEG after enzymatic hydrolysis with sulfatase. A butanol extraction process was performed on the remaining portion to obtain the sample of monoamine transmitters, precursor amino acids, and acidic metabolites. The monoamines and precursor amino acids were finally recovered in HCl solution, while the acidic metabolites shifted into the alkaline buffer from the organic layer. The basic and neutral substances were separated with a 0.1 M sodium citrate/citric acid buffer system (pH 4.0) containing 1% tetrahydrofuran, and the acidic ones with 0.075 M sodium citrate/citric acid buffer (pH 3.5) containing 1% tetrahydrofuran, 10% methanol, and 12% acetic acid. The steady-state concentrations of three monoamine transmitters (noradrenaline, dopamine, and 5-hydroxytryptamine) were determined together with their precursors and metabolites. Changes in the concentrations of these substances were examined for various drugs, of which the effects had been previously confirmed. The changes reflected putative drug effects and demonstrated that the procedure was applicable to the regional determination of monoamines and their metabolically related substances.

Formation and clearance of norepinephrine glycol metabolites in mouse brain

To determine the degree of conversion of 3,4-dihydroxyphenylethyleneglycol (DHPG) to 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and the amount of DHPG eliminated unchanged from the brain, we have examined the kinetics of formation and disappearance of mouse brain MHPG and DHPG following clorgyline (10 mg/kg, i.p.) and/or tropolone (75 mg/kg, i.p.) treatment. During the first 10 min after tropolone, brain DHPG levels accumulated linearly at a rate of 1,300 pmol/g/h, whereas MHPG disappeared exponentially at a rate of 411 pmol/g/h. Following clorgyline administration, brain DHPG declined exponentially at a rate of 1,240 pmol/g/h. In contrast, the elimination of MHPG became a first-order process only when catechol-O-methyltransferase (COMT) was also inhibited in addition to monoamine oxidase. Thus, combined clorgyline and tropolone treatment resulted in an exponential decline of MHPG levels at a rate of 524 pmol/g/h, whereas DHPG levels were slightly but significantly elevated compared to control values. When the animals were treated with pargyline (75 mg/kg, i.p.) in combination with clorgyline and tropolone, brain DHPG and MHPG disappeared at rates of 40 and 660 pmol/g/h, respectively. The above observations suggest that mouse brain DHPG is cleared primarily through O-methylation with minimal direct elimination from brain. Assuming the disposition and clearance of norepinephrine metabolites are similar in mouse and human brain, peripherally measured DHPG in humans is likely derived principally from extracerebral sources and reflects peripheral sympathetic function.

A comparative study of the effects of prostaglandins and d-amphetamine on the metabolism of 3H-dopamine continuously presented to rat brain in vivo

Unanesthetized rats with chronic indwelling cannulas, engaged in food reinforced operant behavior, were infused intracerebroventricularly with a solution containing a trace concentration of 3H-dopamine (3H-DA) with or without prostaglandins (PGs). Approximately 45 minutes after the infusion was started, the procedure was changed to a push-pull perfusion. Perfusate from the ventricles contained significant quantities of the 3H-DA metabolites 3H-3,4-dihydroxyphenylacetic acid (3H-DOPAC), 3H-3-methoxy-4-hydroxyphenylacetic acid (3H-homovanillic acid, 3H-HVA), 3H-3-methoxytyramine (3H-3-MT), and the 3H-noradrenaline (3H-NA) metabolite 3H-3-methoxy-4-hydroxy-phenylethyleneglycol (3H-MHPG). The presence of PGF2 alpha decreased the amount of 3H-DOPAC, 3H-HVA, and 3H-3-MT in perfusate, while PGE1 had the opposite effects. d-Amphetamine (0.5 mg/kg, 1P) affected the recovery of these metabolites from perfusate in a manner similar to PGF2 alpha and opposite to PGE1. PGF2 alpha and the highest (seizure-inducing) dose of PGE1 significantly decreased, while d-amphetamine significantly increased, the quantity of 3H-MHPG in perfusate. Therefore, PGs affect central dopaminergic and noradrenergic activity in vivo, as reflected by changes in their metabolic profiles, and may play a role in the response of the central nervous system to drugs which act through catecholaminergic mechanisms.

Determination of normetanephrine, 3,4-dihydroxyphenylethyleneglycol (free and total), and 3-methoxy-4-hydroxyphenylethyleneglycol (free and total) in rat brain by high-performance liquid chromatography with electrochemical detection and effects of drugs on regional concentrations

A new, fast and sensitive assay for normetanephrine (NM), free and total 3,4-dihydroxyphenylethyleneglycol (DOPEG), and free and total 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG) in brain tissue is described. The method is based on high-performance liquid chromatography with electrochemical detection. Small Sephadex G 10 columns were used for prepurification. This permitted the additional isolation and quantification of tyrosine, 3,4-dihydroxyphenylalanine, noradrenaline, dopamine, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid. The compounds were determined in six brain areas (striatum, cortex, hippocampus, hypothalamus, brainstem, and cerebellum). Most DOPEG and MOPEG in rat brain was present in the conjugated form, except for the cerebellum, where about 80% of MOPEG was nonconjugated. No postmortem effects on MOPEG levels were observed; a slight increase in DOPEG in certain brain areas was found in microwave-killed rats. The effects of clonidine, yohimbine, N,N-dipropyl-5,6-ADTN, and chlorpromazine on the concentrations of the five noradrenaline (NA) metabolites were determined. Free and total DOPEG and MOPEG provide similar information on NA metabolism, whereas NM (after monoamine oxidase inhibition) reflects a different type of interaction of drugs with NA metabolism. The similarity in the pattern of drug-induced changes in NA metabolism in the various brain areas suggests that adrenoreceptors mediating NA metabolism are homogeneously distributed throughout the brain.

The Na,K-ATPase hypothesis for manic-depression. I. General considerations

An hypothesis is presented to explain and integrate experimental and clinical observations on manic-depressive (bipolar or biphasic) psychosis. The model is based on alterations in the activity of the sodium, potassium-activated adenosine triphosphatase (Na, K-ATPase) pump. A reduction in the activity of the Na,K-ATPase can be responsible for both phases of the disorder.

Rat brain norepinephrine metabolism: substantial clearance through 3,4-dihydroxyphenylethyleneglycol formation

To assess whether the metabolic clearance of rat brain norepinephrine (NE) through 3,4-dihydroxyphenylethyleneglycol (DHPG) formation is quantitatively comparable or greater than through 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) production, we studied the accumulation rates of conjugated DHPG and MHPG following probenecid administration in whole brain as well as in several brain regions. Administration of increasing doses of probenecid (100-500 mg/kg, i.p.) 1.5 h before sacrifice produced a dose-dependent increase of conjugated DHPG and MHPG levels. The maximum increment of these conjugated metabolites occurred at a dose of 300 mg/kg or higher. During the first hour following probenecid administration (300 mg/kg, i.p.), rat brain conjugated DHPG and MHPG levels accumulated linearly at a rate of 646 and 319 pmol/g/h, respectively. With the probenecid technique, the estimated appearance rates of conjugated DHPG significantly exceeded those of conjugated MHPG in hypothalamus, midbrain, brainstem, hippocampus, and cerebral cortex. These results clearly indicate that under resting conditions, formation and efflux of conjugated DHPG is the major route of metabolic clearance of rat brain NE.

Relative importance of 3-methoxy-4-hydroxyphenylglycol and 3,4-dihydroxyphenylglycol as norepinephrine metabolites in rat, monkey, and humans

A gas chromatographic-mass spectrometric assay, which allowed simultaneous measurement of 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG), was used to show that the concentration of MHPG in primate CNS far exceeded that of DHPG and that both metabolites were mainly in the unconjugated form. In rat brain, DHPG concentration was generally higher than that of MHPG, and both existed predominantly as conjugates. Rat and primate plasma contained more MHPG than DHPG. In plasma of primates but not of rats, higher proportions of the metabolites were conjugated, compared to those in brain. Significant correlations existed between MHPG and DHPG in rat brain, monkey brain, human plasma, and both monkey CSF and plasma. In monkeys, a significant CSF-plasma correlation was found for MHPG, but not for DHPG. Acute administration of piperoxane raised rat brain MHPG and DHPG concentration; desipramine prevented this rise in DHPG, but not in MHPG. Desipramine alone decreased DHPG, but not MHPG, concentration. Piperoxane increased monkey brain MHPG, but not DHPG, concentration. These data suggest that DHPG is a valuable metabolite to measure when assessing norepinephrine metabolism in the rat. Under certain conditions, measurement of rat brain MHPG and DHPG may provide information concerning the site of norepinephrine metabolism. However, in primates the importance of monitoring DHPG, in addition to MHPG, is uncertain.

Measurement of tritiated norepinephrine metabolism in intact rat brain

A procedure for the study of NE metabolism in the intact rat brain is described. The method involves ventriculocisternal perfusion of the adult male rat with artificial CSF containing [3H]NE. Radioactivity in the perfusate associated with NE and its metabolites 3,4-dihydroxymandelic acid (DOMA), 3,4-dihydroxyphenylethyleneglycol (DHPG), 3-methoxy-4-hydroxymandelic acid (VMA), 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), and normetanephrine (NMN) is separated using high-performance liquid chromatography (HPLC). After 80 min the radioactivity in the perfusate reaches an apparent steady-state. Analysis of the steady-state samples shows higher activity in the fractions corresponding to DHPG and MHPG than in those corresponding to DOMA and VMA, confirming glycol formation as the major pathway of NE metabolism in rat brain. Pretreatment with an MAO inhibitor (tranylcypromine) results in a marked decrease in the deaminated metabolites DHPG and MHPG and a concurrent increase in NMN. The results indicate this to be a sensitive procedure for the in vivo determination of changes in NE metabolism.

A radioenzymatic technique for the measurement of free and conjugated 3,4-dihydroxyphenylethylene-glycol in brain tissue and biological fluids

A simple, sensitive and specific radioenzymatic assay for the measurement of 3,4-dihydroxyphenylethyleneglycol (DOPEG) was developed. The assay is based on the conversion of the compound to its O-methylated derivative in the presence of catechol-O-methyltransferase and [3H]S-adenosyl-methionine. The tritiated 3-methoxy-4-hydroxyphenylethyleneglycol formed is selectively extracted in organic solvents and isolated by thin layer chromatography. After oxidation to vanillin the O-methylated compound is extracted and measured by liquid scintillation spectrophotometry. This assay has been applied to the measurement of free and conjugated DOPEG in a variety of biological tissues and fluids. Both free and conjugated DOPEG were readily detected in discrete rat brain areas. Substantial amounts of free and conjugated DOPEG were also measured in ventricular perfusates from freely moving rats. Finally, the presence of DOPEG was also demonstrated in human cerebrospinal fluid, plasma and urine. Only the free form of DOPEG was found in cerebrospinal fluid, whereas both unconjugated and conjugated forms were present in plasma and urine.

Brain 3,4-dihydroxyphenylethyleneglycol levels are dependent on central noradrenergic neuron activity

The effect of manipulations aimed to alter brain noradrenergic neuron activity on the levels of free and conjugated DOPEG in discrete brain areas was studied in the rat. Electrical stimulation of the medial forebrain bundle for 10-20 min produced a frequency dependent elevation of free and conjugated DOPEG concentrations in the anterior cerebral cortex and in the hippocampus. In contrast, acute interruption of noradrenergic nerve impulse flow by application of tetrodotoxin (50-100 ng) into the medial forebrain bundle markedly diminished cortical and hippocampal DOPEG levels at 0.5-2 h post-injection. Cortical conjugated and free DOPEG levels were also reduced (by 80-96%) 2-3 weeks after bilateral electrolytic lesion of the locus coeruleus, 6-hydroxydopamine-induced lesion of the ascending noradrenergic pathways or noradrenergic denervation by the neurotoxic agent DSP4. Finally, the alpha-adrenoceptor blocking agents yohimbine (1-10 mg/kg, ip) and RX 781094 (3-10 mg/kg, ip) increased whereas the alpha-adrenergic agonist clonidine (0.01-1 mg/kg, sc) decreased DOPEG levels in the cerebral cortex, hypothalamus and septal areas. These data indicate that free and conjugated DOPEG formation is dependent on, and may serve as an index of, central noradrenergic neuron activity.

Maternal smoking and elevation of catecholamines and metabolites in the amniotic fluid

To assess the effect of maternal smoking on fetal adrenergic activity, simultaneous measurements in amniotic fluid of the parent catecholamines, dopamine (DA), norepinephrine (NE), and epinephrine (E), as well as the specific intraneuronal deaminated metabolites of DA, 3,4-dihydroxyphenylacetic acid (DOPAC), and of NE, 3,4-dihydroxyphenylglycol (DOPEG), were made by radioenzymatic assay. In the second trimester, a significant (p less than 0.002) and selective elevation of the mean DOPEG concentration was noted in the amniotic fluid of smokers (N = 8) as compared to nonsmokers (N = 36). In the third trimester, significant elevations were found in the mean amniotic fluid concentration of E (p less than 0.0002) and NE (p less than 0.0005), as well as DOPEG (p less than 0.0002), of smokers (n = 12) when compared to nonsmokers (N = 12). There were no significant differences in amniotic fluid concentrations of DA and its deaminated metabolite DOPAC. Since compartmentalization of catecholamines exist between the maternal and fetal circulations, the elevated levels of NE, E, and DOPEG in the amniotic fluid of smokers suggests fetal adrenergic activation as a result of fetal hypoxia and/or by a direct effect of nicotine on the fetal adrenergic system.

Amniotic fluid catecholamines and metabolites in intrauterine growth retardation

Simultaneous determinations of amniotic fluid levels of the catecholamines dopamine (DA), norepinephrine (NE), and epinephrine (E), and the intraneuronal metabolites of DA, 3,4-dihydroxyphenylacetic acid (DOPAC) and NE, 3,4-dihydroxyphenylglycol (DOPEG), were made, by radioenzymatic assay, in pregnancies resulting in growth-retarded (n = 14) and normal (n = 63) infants. Significant elevations in the mean concentration of NE (p less than 0.000005), E (p less than 0.005), and DOPEG (p less than 0.000001) as well as a significant decrease in the mean concentration of DOPAC (p less than 0.000001) were found in pregnancies resulting in growth-retarded infants as compared to pregnancies resulting in normal infants. Amniotic fluid DOPEG levels were found to be the most discriminative. As amniotic fluid catecholamines are predominantly of fetal origin, these findings suggest that an increase in adrenergic activity and a decrease in dopaminergic activity occur in intrauterine growth retardation as a response to chronic stress.

Rat brain and plasma norepinephrine glycol metabolites determined by gas chromatography-mass fragmentography

A gas chromatographic-mass fragmentographic (GC-MF) procedure is described for the simultaneous quantitation of 3,4-dihydroxyphenylethyleneglycol (DHPG) and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) in brain tissue and plasma. DHPG and MHPG were assayed as their respective acetyl-trifluoroacyl esters, using [2H2]DHPG and [2H3]MHPG as internal standards. Assay sensitives of at least 1 ng per sample were attainable for the quantitation of free glycols, whereas for determination of total DHPG, assay sensitivity was 2.5 ng. Whole rat brain total (99.2 +/- 4.11 ng/g) and free (13.0 +/- 1.14 ng/g) DHPG concentrations were similar to respective total (86.0 +/- 3.70 ng/g) and free (12.3 +/- 0.41 ng/g) MHPG levels. Total DHPG concentrations exceeded total MHPG levels in hypothalamus (3.0:1), midbrain (1.4:1), pons plus medulla (1.3:1), and hippocampus (1.5:1), whereas in other brain regions the levels of these metabolites were similar. In plasma, however, total DHPG levels were only 20% as high as MHPG concentrations. In mouse brain, DHPG and MHPG occurred almost entirely in free form (greater than 90%), but total DHPG levels were only 50% as high as respective MHPG concentrations. These results emphasize the substantial formation of DHPG compared with MHPG in rat and mouse brain and suggest that DHPG formation and efflux may be of equal or greater importance than MHPG in the metabolic clearance of CNS norepinephrine in some species.

An increase in catecholamines and metabolites in the amniotic fluid compartment from middle to late gestation

By means of a modified radioenzymatic assay, simultaneous determinations of the parent catecholamines, epinephrine (E), norepinephrine (NE), and dopamine (DA), and their deaminated metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylglycol (DOPEG), were made in amniotic fluid obtained during the second (N = 44) and third (N = 20) trimesters of normal pregnancies. Significant positive correlations were noted between gestational age and concentrations of E, NE, DA, DOPAC, and DOPEG in amniotic fluid. These findings provide evidence of progressive fetal adrenergic maturation through pregnancy. In addition, our data suggest a parallel maturational event in the central nervous and peripheral catecholamine systems of the fetus, since DOPAC and DOPEG are more representative of catecholamine neuronal activity in the brain.

Presynaptic receptor systems on the noradrenergic neurones of rat brain

A simple volume averaging model was shown to be inadequate for predicting effective computed tomographic attenuation values of mixtures of bone or air with soft tissue. Computed tomographic values derived from scanning stratified sub-slice thickness objects were shown theoretically and experimentally to have a non-linear dependency on relative fractional content and a surprisingly large dependency on spatial extent of the stratified substances. The mode was applied to the problem of computed tomographic values in thin, flat structures such as pools of blood in the subarachnoid space. The results show only small deviations from simple volume averaging theory for layers of low contrast substances such as blood and soft tissue, but potentially large deviations for layers of substances with high contrast differences such as bone, air, and tissue. This phenomenon explains certain artifacts and demonstrates rather fundamental problems in the accuracy of analytic reconstruction techniques. It may justify postprocessing correction or iterative approaches.

Metabolism of 3H-dopamine continuously perfused through push-pull cannulas in rats' brains: modification by amphetamine or prostaglandin F2 alpha

Using perfusion cannulas implanted in the lateral cerebroventricles, the metabolism of a trace concentration of 3H-dopamine, continuously presented, was investigated in rats performing an operant for food reinforcement. The subjects were mature, drug-naive, male Long-Evans rats. Perfusate contained measurable quantities of 3H-3,4-dihydroxyphenylacetic acid (3H-DOPAC), 3H-3-methoxy-4-hydroxyphenylacetic acid (3H-homovanillic acid, 3H-HVA), 3H-3-methoxytyramine (3H-3-MT) and the 3H-noradrenaline metabolite, 3H-3-methoxy-4-hydroxyphenylethyleneglycol (3H-MHPG). Systemic injection of d-(1.5 mg/kg) or 1-(3.0 mg/kg) amphetamine resulted in decreased quantities of 3H-DOPAC, 3H-HVA and 3H-MHPG in perfusate with a concurrent decrease in fixed-ratio 20 behavior. Addition of prostaglandin F2 alpha (10 ng/microliters perfused at a rate of 10 microliters/minute) had no effect on the rats' fixed-ratio 20 behavior or rectal temperature, but resulted in decreased quantities of 3H-DOPAC, 3H-HVA and 3H-MHPG in perfusate. It is concluded that this methodology allowed us to monitor drug-induced changes in CNS dopaminergic and noradrenergic function in conscious rats engaged in schedule-controlled operant behavior. Furthermore, a trace concentration of PGF2 alpha in perfusion medium caused changes in 3H-dopamine metabolism in a manner similar to that of systemically administered amphetamines.

Dopamine modulation of acetylcholine release from the guinea-pig brain

The effect of dopamine (DA) and apomorphine (Apo) on acetylcholine (ACh) release from guinea-pig brain was investigated (i) in superfused slices of cerebral cortex, caudate nucleus, tuberculum olfactorium, brain stem and (ii) in unrestrained, unanaesthetized animals, provided with epidural parietal cups. DA reduced the ACh release only from slices of caudate nucleus, whereas Apo was also effective in the cerebral cortex. DA and Apo inhibition in caudate nucleus was antagonized by spiroperidol. The injection of DA (1.5 and 5 micromoles) into the cerebral ventricles (i.c.v.) caused a late, moderate behavioural stimulation and enhanced ACh outflow from the parietal cortex. The injection of Apo, either i.c.v. or i.p., promptly elicited similar effects. Spiroperidol 0.5--2 mg/kg i.p. counteracted the behavioural stimulation by Apo and amphetamine, but unexpectedly enhanced the cortical ACh outflow, leaving unaffected the cholinergic responses to Apo and Amphetamine. These results show that DA directly hinders ACh release from the striatal cholinergic structures surviving in vitro, via classical neuroleptic-sensitive receptors. On the other hand, the enhanced cortical ACh outflow caused by DA and DA-mimetic drugs in the unanaesthetized animals is suggestive of a disinhibition of the corticopetal cholinergic neurones, via neuroleptic-insensitive mechanisms. Hence, the 'paradoxical' effect of spiroperidol might represent the consequence of the increased activity of nigral DA cells with collaterals possibly involved in the control of the ascending cholinergic pathways.

3-Methoxy-4-hydroxyphenethyleneglycol production by human brain in vivo

A direct method has been employed to estimate the rate of production by human brain of 3-methoxy-4-hydroxyphenethyleneglycol, the major metabolite of brain norepinephrine, a brain neurotransmitter. Venous specimens were obtained from the internal jugular vein from ten awake human subjects at a puncture site above the common facial vein, the first major source of extracranial inflow. Arterial specimens were simultaneously obtained from the radial artery. Plasma samples were assayed and a highly significant difference was found in the concentration of the metabolite in plasma coming out of the brain (venous blood) as compared to plasma entering the brain (arterial blood). This venous-arterial difference was calculated to be 0.7 +/- 0.1 nanogram per milliliter of blood. Assuming an adult brain weight of 1400 grams and normal cerebral blood flow, it is estimated that the rate of production of 3-methoxy-4-hydroxyphenethyleneglycol by the awake human brain is approximately 597 nanograms per minute or 35.8 micrograms per hour. Urine specimens were also collected from six of these subjects during a period of 1 to 3.5 hours, which bracketed the time the blood samples were obtained. For these six subjects the output of 3-methyoxy-4-hydroxyphenethyleneglycol by whole brain was estimated to be 40.9 micrograms per hour, whereas the rate of its excretion into urine was 64.5 micrograms per hour.

The effect of acute and chronic desipramine and amitriptyline treatment on rat brain total 3methoxy-4-hydroxyphenylglycol

The effect of acute (single dose), short-term (4 days), and chronic treatment (21 days) with two tricyclic antidepressants desipramine and amitriptyline on brain 3-methoxy-4-hydroxyphenylglycol (MHPG) was examined in the rat. Amitriptyline had no effect on brain total MHPG irrespective of the duration of the treatment and did not interfere with the lowering effect of clonidine on brain total MHPG. Acute and short-term desipramine treatment decreased brain total MHPG in rats, while chronic desipramine treatment increased it. The differential effect of acute and chronic treatment of desipramine on the brain total MHPG was further demonstrated by the lack of interference with the lowering effect of clonidine on brain total MHPG by one single dose of desipramine; partial interference after 4 days and complete interference after 21 days of desipramine treatment.

Brain self-stimulation: direct evidence for the involvement of dopamine in the prefrontal cortex

Rats were trained to self-stimulate the medial prefrontal cortex, a region rich in dopaminergic terminals. After the region adjacent to the electrode site was labeled with [14C]dopamine, it was perfused repeatedly by means of push-pull cannulas. Electrical stimulation of this cortical area in six animals enhanced the release of dopamine and its associated metabolites in nine of 16 experiments. Thus in vivo evidence is provided that dopamine is involved in the brain self-stimulation mechanism within the frontal cortex.

Hypothalamic adrenaline synthesis after stimulation of the medial forebrain bundle

1 The problem of whether locally released noradrenaline can be methylated to adrenaline in the hypothalamus has been investigated. 2 During stimulation of the medial forebrain bundle (MFB) the hypothalamic adrenaline content increased somewhat, but the increase was not statistically significant (13%, mean of 10 experiments). 3 After inhibition of the activity of monoamine oxidase and catechol-O-methyltransferase this increase was much larger (80%, mean of 9 experiments). 4 Adrenalectomy did not prevent the rise in hypothalamic adrenaline after stimulation of the MFB. These results suggest that noradrenaline released during activity of noradrenergic hypothalamic structures may be methylated to adrenaline in the hypothalamus.

Axoplasmic transport of norepinephrine in the locus coeruleus-hypothalamic system in the rat

The axoplasmic transport of norepinephrine (NE) between the nucleus locus coeruleus (LC) and the hypothalamus has been measured by three methods which employ the stereotaxic injection of [3H]catecholamines in the rat brain. [3H]NE is synthesized from [3H]dopamine (DA) injected into the LC and transported at a rate of 0.8-0.9 mm/h. This rate is probably an underestimate since it includes the time required for uptake and conversion of [3H]DA to [3H]NE prior to transport. Measurement of transport of [3H]NE between the posterior and anterior hypothalamus gives a rate of 2 mm/h which is independent of [3H]DA uptake and [3H]NE synthesis. This rate is in good agreement with the 1.9 mm/h figure calculated for [3H]NE transport in the system after LC injection of [3H]NE and represents a closer estimate of the true rate of axoplasmic transport than the 0.8-0.9 mm/h estimate. Transport of [3H]NE occurs through primarily ipsilateral NE fibers running in the median forebrain bundle and is blocked by 6-hydroxydopamine lesions in the bundle. Early appearing [3H]NE in the hypothalamus forms a relatively stable pool which is unaffected by median forebrain bundle lesions and is essentially unchanged by [3H]NE transported from the LC. This pool appears to be derived from non-specific spread of [3H]DA after injection, probably through the cerebrospinal fluid.

A method for the assay of conjugated 3,4-dihydroxyphenylglycol, a major noradrenaline metabolite in the rat brain

We present the first published procedure for the measurement of endogenous conjugated 3,4-dihydroxyphenylglycol (DOPEG) in the rat brain. Conjugated DOPEG is estimated from brain extracts after enzymic hydrolysis, isolation of hydrolysed DOPEG on alumina, methylation of DOPEG to 3-methoxy-4-hydroxyphenylglycol (MOPEG) and gas chromatographic quantification of MOPEG. The level of conjugated DOPEG in the CNS of rats (65.7 +/- 0.7 ng/g whole brain tissue corrected for recovery) almost equals the level of conjugated MOPEG. The sensitivity of the method is about 6 ng/g brain tissue. After inhibition of monoamine oxidase with clorgyline (30 mg/kg) conjugated DOPEG and MOPEG both disappeared from the brain with a half-life of about 1 h. Turnover calculations indicate that conjugated DOPEG and MOPEG are the two major noradrenaline end-metabolites in the rat brain. The method of estimating conjugated DOPEG also allows the measurement of noradrenaline, dopamine and total MOPEG in an extract from one half of a rat brain.