Determination of catecholamines in tissue and body fluids using microbore HPLC with amperometric detection

High performance liquid chromatography method for the detection of released purinergic and biogenic amine signaling molecules from in vitro ileum tissue

Adenosine triphosphate (ATP) and serotonin (5-HT) are known to play key roles in the function and activity of the gastrointestinal tract; however, no methods have been established for the monitoring of these signaling molecules within one assay. We have developed a simple chromatographic methodology using UV/visible detection for the analysis of purinergic and biogenic amine signaling molecules. The chromatographic separation was achieved in an isocratic mode, where the mobile phase consisted of 5% methanol and 95% ammonium phosphate buffer with 10 mM tetrabutylammonium bisulfate. Column temperature of 45 degrees C provided the means to separate all analytes within 14.7 min. Good resolution and tailing factors were observed for all components within the separation. The LOD for ATP and 5-HT was 30 and 317 nM, respectively, with a linear range from 10-0.02 microM. In vitro measurements were carried out by using aliquots from the buffer the tissue was stored in after 30 min to measure released molecules. In vitro assay of ileum tissue in the presence and absence of endogenous ATP was carried out. Results showed that ATP can elevate 5-HT release. This method can be used to study alterations in these key signaling molecules with gastrointestinal disease.

Hydroquinone-based derivatization reagents for the quantitation of amines using electrochemical detection

Two new reagents, NDTE (2,5-dihydroxyphenylacetic acid, 2,5-bis-tetrahydropyranyl ether p-nitrophenyl ester) and HLTE (homogentisic gamma-lactone tetrahydropyranyl ether), are described for the chemical derivatization of primary and/or secondary amines to form an electrochemically active product. These reagents undergo reaction with the aforementioned analytes to form a product possessing the hydroquinone moiety, thus allowing for reversible electrochemical detection at mild oxidation potentials. The reactivity of each reagent was demonstrated by using N-ethylbenzylamine (EBzA) and the dipeptide isoleucine leucine methyl ester as model analytes. The investigation included the isolation and identification of the intermediates and final products from derivatization of EBzA. These isolated standards were subsequently characterized with respect to electrochemical properties by means of cyclic voltammetry. In LC-EC experiments, the concentration limit of detection (CLOD) of the purified EBzA product was determined to be 5 nM (100 fmol) at a detection potential of +200 mV vs Ag/AgCl ([Cl-] = 3 M). The CLOD values obtained by LC-EC after derivatization of aqueous solutions of EBzA and Ile-Leu-OMe with NDTE were 25 nM (250 fmol) and 250 nM (2.5 pmol), respectively.

The assay of the catecholamine content of small volumes of human plasma

Plasma catecholamines are routinely measured using high-performance liquid chromatography (HPLC) with electrochemical detection. Most of the present assays require sample volumes of at least 500 microL and are complex and labour-intensive procedures, or require large capital investment to reduce the sample size. This paper describes a liquid/liquid plasma catecholamine extraction procedure, HPLC separation and electrochemical detection method which is simple, sensitive and reproducible. The resting catecholamine concentration of 50 microL adult human plasma can be assayed using standard electrochemical detection. The limits of detection were 0.1 fmol injected onto the column for each catecholamine. This method allows the routine assay of plasma catecholamine concentrations within the normal adult ranges in both 500 and 50 microL samples. The within assay coefficient of variation (CV) for noradrenaline (NA) was 1.2% in 500 microL plasma and 1.9% for 50 microL plasma, corresponding values for adrenaline (A) were 8.5 and 6.6%. The between assay CVs were 3.9 and 7.8% for NA, and 9.9 and 5.7% for A.

Microdialysis update: optimizing the advantages

Microdialysis was introduced in the early 1970s as a method to measure dynamic release of substances in the brain (see Tossman & Ungerstedt, 1986). The technique has been refined over the past three decades due to the development of new materials for dialysis membranes and commercial availability of smaller, more consistently fabricated probes. A typical microdialysis probe consists of rigid metal concentric tubing with a semipermeable region at the tip (Fig. 1). Molecules of restricted size passively diffuse from the brain through the dialysis membrane into an infusion solution which is then directed out of the brain and collected in tubes for serial analysis of substance content. Probes are inserted into the brain region of interest, typically making lesions during their travel through the brain and at the sampling site. Once the trauma of insertion subsides, usually after an hour or so, probes collect substances released from axons projecting to dendrites and cell bodies of the targeted area. Substances surrounding the semipermeable region of the probe passively diffuse down a concentration gradient into the solution infused through the probe. Substance recovery from the brain decreases exponentially with faster infusion rates. A high precision infusion pump is critical for maintaining constant flow through the probes to ensure that altered substance content in the dialysates reflects changes in release by the brain and not variable diffusion gradients resulting from sporadic changes in flow rates through the probes. High performance liquid chromatography (HPLC) is commonly used to measure target substances in the dialysates, but other methods such as radioimmunoassay may be employed. The development of microbore columns for HPLC (Durkin et al. 1985) and their commercial availability by the mid 1990s has made it possible to accurately measure smaller amounts of substances in the dialysates.

Procedure for the sample preparation and handling for the determination of amino acids, monoamines and metabolites from microdissected brain regions of the rat

A method is described for the analysis of amino acids, monoamines and metabolites by high-performance liquid chromatography with electrochemical detection (HPLC-ED) from individual brain areas. The chromatographic separations were achieved using microbore columns. For amino acids we used a 100x1 mm I.D. C8, 5 microm column. A binary mobile phases was used: mobile phase A consisted of 0.1 M sodium acetate buffer (pH 6.8)-methanol-dimethylacetamide (69:24:7, v/v) and mobile phase B consisted of sodium acetate buffer (pH 6.8)-methanol-dimethylacetamide (15:45:40, v/v). The flow-rate was maintained at 150 microl/min. For monoamines and metabolites we used a 150X1 mm I.D. C18 5 microm reversed-phase column. The mobile phase consisted of 25 mM monobasic sodium phosphate, 50 mM sodium citrate, 27 microM disodium EDTA, 10 mM diethylamine, 2.2 mM octane sulfonic acid and 10 mM sodium chloride with 3% methanol and 2.2% dimethylacetamide. The potential was +700 mV versus Ag/AgCl reference electrode for both the amino acids and the biogenic amines and metabolites. Ten rat brain regions, including various cortical areas, the cerebellum, hippocampus, substantia nigra, red nucleus and locus coeruleus were microdissected or micropunched from frozen 300-microm tissue slices. Tissue samples were homogenized in 50 or 100 microl of 0.05 M perchloric acid. The precise handling and processing of the tissue samples and tissue homogenates are described in detail, since care must be exercised in processing such small volumes while preventing sample degradation. An aliquot of the sample was derivatized to form the tert.-butylthiol derivatives of the amino acids and gamma-aminobutyric acid. A second aliquot of the same sample was used for monamine and metabolite analyses. The results indicate that the procedure is ideal for processing and analyzing small tissue samples.

Improved detection limit for catecholamines using liquid chromatography-electrochemistry with a carbon interdigitated array microelectrode

The detection limit of catecholamines can be lowered by using a carbon-based interdigitated array (IDA) microelectrode as a detector for liquid chromatography (LC). The IDA electrode is more sensitive than conventional glassy carbon electrodes due to the high current density caused by radial diffusion at each microband, and redox cycling between two microband arrays. Since the number of redox cycles increases at lower flow-rates, the carbon IDA is particularly useful for microbore LC. In an LC system with a 1-mm microbore column and a carbon IDA electrode, the peak height of dopamine (DA) and DOPAC did not decrease with decreasing flow-rate because of this redox cycling. A low detection limit of 5 fg (32 amol) and 9.6 fg (57 amol) was obtained for DA and DOPAC due to the high current density and low background noise level (0.1 pA) at the carbon IDA electrode. The total charge generated by oxidizing DA at the anodic array was more than the value calculated by assuming that all the DA molecules were oxidized.

Acetylcholine measurement of cerebrospinal fluid by in vivo microdialysis in freely moving rats

Acetylcholine (ACh) and choline (Ch) levels in rat cerebrospinal fluid (CSF) were determined by in vivo microdialysis (CSF microdialysis) in both halothane-anesthetized and freely-moving rats. The Ch/ACh ratio in CSF perfused with Ringer's solution (30 microliters/30 min) containing 10(-5) M physostigmine, a centrally active cholinesterase inhibitor, was significantly lower than that in unprocessed CSF due to significantly higher ACh levels in the former. The successive measurement on the 2nd and 7th day after the guide cannula implantation demonstrated the feasibility of the CSF microdialysis method for repetitive monitoring of CSF ACh and Ch levels in freely moving rats without extensive tissue damage. Intraperitoneal administration of physostigmine caused an increase in CSF ACh levels, whereas administration of neostigmine, which cannot penetrate into the blood brain barrier, did not. Furthermore, a centrally active acetylcholinergic M1-receptor agonist, AF102B, produced an increase in CSF ACh and Ch levels. Thus, the present study demonstrates that CSF microdialysis is a useful method for evaluating overall central cholinergic activity and investigating the pharmacological effects of various drugs that act via the central cholinergic system.

Effect of in vivo He-Ne laser irradiation on biogenic amine levels in rat brain

In order to elucidate the metabolic modifications induced in rat brain by low power He-Ne laser irradiation in vivo, the variations in the biogenic amine levels in cortex, striatum and hippocampus were studied. Noradrenaline (NA), dopamine (DA) and serotonin (5-HT) were evaluated by HPLC-EC on irradiated rats, untreated rats (controls) and rats which had undergone restraint stress (stressed). The results obtained on groups of four to eight rats assayed individually showed that irradiation caused a strong increase in 5-HT in striatum and hippocampus, a small but significant decrease in NA in cortex, and DA levels were not significantly affected. Restraint stress per se led to a considerable decrease in 5-HT and DA in striatum and hippocampus, but did not significantly alter the NA levels.

Plasma catecholamines--analytical challenges and physiological limitations

Catecholamines in plasma may be measured to assess sympathoadrenal activity. Numerous assay methodologies have been published, illustrating the fact that there are many analytical problems. Different methodologies are discussed briefly. A plea for better validation, especially with regard to specificity (which should not be confused with sensitivity or reproducibility), is made. Plasma NA is a frequently used marker for sympathetic nerve activity in humans, but the data obtained are often misinterpreted due to lack of appreciation of the physiological determinants of the NA concentration measured. NA overflow from an organ gives a good reflection of nerve activity in that organ. However, sympathetic nerve activity is highly differentiated, particularly during stress, and conventional plasma NA levels (usually forearm venous samples) cannot be taken as an indication of 'sympathetic tone' in the whole individual. NA is rapidly removed from plasma, resulting in meaningless net veno-arterial concentration differences over organs unless its removal from arterial plasma is taken into account. In the forearm, for example, 40-50% of catecholamines are removed during one passage; about half of the NA in a venous sample is derived from the arm and half from the rest of the body. Therefore, conventional venous sampling overemphasizes local (mainly skeletal muscle) nerve activity. Whole-body sympathetic nerve activity may be monitored in arterial or mixed venous (i.e. pulmonary arterial) samples, which reflect NA overflow from all organs in the body. NA levels are determined both by overflow to plasma and clearance from plasma. NA turnover studies with 3H-NA infusions may be needed to assess clearance, but the simpler concentration measurements usually yield adequate information if the sampling site is relevant. NA overflow from an organ can be assessed (using 3H-NA or ADR as a marker for NA extraction in the organ) and provides valuable information on local sympathetic activity. Mental stress elicits marked circulatory responses, with mainly cardiorenal sympathetic activation and minor elevations of conventional venous plasma NA levels, thus illustrating the differentiated firing pattern of the sympathetic nerves. Circulating ADR is less important than neurogenic mechanisms in the responses to stress. Concentration-effect studies for infused catecholamines may be used for receptor sensitivity studies in vivo, but reflexogenic contributions to responses need to be determined. However, prejunctional mechanisms cannot be assessed without knowledge of the nerve activity present; for example, ADR infusion leads to increased nerve activity. When correctly sampled, measured and interpreted, plasma catecholamines can yield very valuable information on sympathoadrenal activity.

Preparation of an optimum mobile phase for the simultaneous determination of neurochemicals in mouse brain tissues by high-performance liquid chromatography with electrochemical detection

A systematic method is described for the optimization of a mobile phase for the simultaneous determination of 24 neurochemicals consisting of catecholamine, serotonin, their precursors and metabolites and related materials. This mobile phase contained sodium acetate (0.04 M), citric acid (0.01 M), sodium chloride (0.0126 M), sodium octyl sulfate (91 mg/l), tetrasodium EDTA (50 mg/l) and 10% (v/v) methanol. When this optimum mobile phase was applied to the analysis of brain tissues of the Swiss male mouse, twelve neurochemicals were quantified in the free state: tyrosine, L-beta-3,4-dihydroxyphenylanine, dopamine, 3,4-dihydroxyphenylacetic acid, 4-hydroxy-3-methoxyphenylacetic acid, norepinephrine, 3-methoxy-4-hydroxyphenylglycol, DL-3,4-dihydroxymandelic acid, DL-4-hydroxy-3-methoxymandelic acid, serotonin, L-tryptophan, 5-hydroxyindole-3-acetic acid and DL-synephrine and normetanephrine, appearing as a fused peak. This fused peak was present on the chromatogram tracings of all the mouse brain tissues. The separable neurochemicals not found by this procedure in the Swiss male mouse tissues were DL-3,4-dihydroxyphenylglycol,5-hydroxytryptophan, epinephrine, DL-octopamine, metanephrine, deoxyepinephrine, homovanillyl alcohol, N-acetylserotonin, tyramine and 3-methyltyramine.

High performance liquid chromatography as a tool in the definition of abnormalities in monoamine and tryptophan metabolites in cerebrospinal fluid from patients with neurological disorders

In this study we report the levels of 3-methoxy-4-hydroxyphenylglycol, 3,4-dihydroxyphenylacetic acid, homovallinic acid, tryptophan, 5-hydroxyindole-3-acetic acid and serotonin in lumbar cerebrospinal fluid (CSF) from patients with multiple sclerosis, cerebrovascular disease and muscular tension headache the later, as healthy controls. The separation of these substances was performed on a reversed phase column by ion pair high performance liquid chromatography and detection was made by a glassy carbon electrode set at +900 mV vs Ag+/AgCl. The whole separation was achieved within 25 min. Concentrations of all substances (10-1000 pmole/L) were linearly proportional to areas obtained. The system is sensitive, stable and reproducible. The significance of CSF levels of these metabolites from patients groups compared with healthy controls are discussed.

Chronic neurochemical and behavioral changes in MPTP-lesioned C57BL/6 mice: a model for Parkinson's disease

The long-term effect of the parkinsonism inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on pre- and postsynaptic structures of the nigrostriatal and mesolimbic dopamine (DA) system in adult C57BL/6 mice (2 x 40 mg/kg s.c.) was investigated using neurochemical and behavioral methods. It was found that MPTP induced a severe depletion of striatal DA levels (-80%) that persists for 4 weeks after treatment, with less severe effects in nucleus accumbens (-36%) and the olfactory tubercle (-52%). These depletions are associated with decreased tyrosine hydroxylase (TH) activity as determined in vivo and increased turnover of DA. MPTP treatment did not induce any change in the DA2-receptor as determined by [3H]spiperone binding or by two different behavioral tests, i.e. apomorphine-induced climbing and apomorphine-induced stereotypies. No significant weight loss during 4 weeks after MPTP was found. The spontaneous motor activity in these mice was profoundly and persistently depressed (-66%) as a result of the MPTP-induced DA denervation and the motor deficit was completely reversed by L-DOPA treatment. We suggest that MPTP-treated C57BL/6 mice may serve as a suitable model for Parkinson's disease.

Plant-derived neurotoxic amino acids (beta-N-oxalylamino-L-alanine and beta-N-methylamino-L-alanine): effects on central monoamine neurons

In the present study the subacute effects of beta-N-oxalylamino-L-alanine (BOAA) and beta-N-methylamino-L-alanine (BMAA) on CNS monoamine neurons in rats were investigated following intracisternal injections or local intracerebral administration into substantia nigra. In vitro effects of BOAA and BMAA on high-affinity synaptosomal uptake of dopamine (DA), noradrenaline (NA), and serotonin (5-HT) were also examined. Intracisternal administration of BMAA decreased NA levels in hypothalamus, whereas no effects were seen on DA or 5-HT levels. Following intranigral injections of BOAA, NA levels tended to decrease in several regions, whereas the DA levels and the levels of DA metabolites were unaffected in all regions analyzed. Loss of tyrosine hydroxylase (TH) immunoreactivity in the intranigral injection sites and the presence of TH-immunoreactive pyknotic neurons near the borders of the injection sites were observed following both BOAA and BMAA treatments. Furthermore, substance P-immunoreactive terminals in substantia nigra pars reticulata were also found to have disappeared within the lesioned area following either BOAA or BMAA injections. Incubations with both BOAA and BMAA (10(-5) M) reduced high-affinity [3H]NA uptake in cortical synaptosomes to 69% and 41% of controls, respectively, whereas the striatal high-affinity [3H]DA uptake and the cortical high-affinity [3H]5-HT uptake were unaffected by BOAA or BMAA. The results demonstrate that both BOAA and BMAA can affect central monoamine neurons, although the potency and specificity of these substances on monoamine neurons when administered acutely into cerebral tissue or liquor cerebri seem to be low. However, the in vitro studies indicate selective effects of both compounds on NA neurons in synaptosomal preparations.

Qualitative and quantitative high performance liquid chromatographic analysis of monoamine neurotransmitters and metabolites in cerebrospinal fluid and brain tissue using reductive electrochemical detection

The application of reductive coulometric electrochemical detection for analysis of the monoamine neurotransmitters norepinephrine, dopamine, and serotonin and their common metabolites in brain and cerebrospinal fluid following separation by isocratic high performance liquid chromatography is described. The high sensitivity and screening capabilities of coulometric electrodes permits the accurate quantitation of as little as 3-5 pg of these compounds in tissue following a simple single step purification procedure. Moreover, comparison of peak height ratios obtained from analysis of authentic reference standards and tissue samples at selected multiple electrode potentials provides a straightforward means for qualitative evaluation of peak identification and purity during analysis of biological samples. The method is comparatively inexpensive and precise within and between day coefficients of variation for most compounds range from 2-5%. Thirty samples can be run in duplicate in a 24 h period.

Studies on brain monoamine and neuropeptide systems after neonatal intracerebroventricular 6-hydroxydopamine treatment

In order to study the effects of a neonatal dopamine lesion on dopaminergic, serotonergic and peptidergic systems, Sprague-Dawley rats were treated by intracerebroventricular administration of 6-hydroxydopamine (100 micrograms, days 3 and 6) following desipramine pretreatment (25 mg/kg s.c.). At 60-70 days postnatally a profound reduction of dopamine- and 3,4-dihydroxyphenylacetic acid levels was found in striatal and limbic forebrain regions concomitant with an extensive loss of tyrosine hydroxylase-immunoreactive fibers, while no significant alteration in noradrenaline levels was seen. A marked loss of tyrosine hydroxylase-immunoreactive cell profiles was also observed in the substantia nigra and ventral tegmental area in mesencephalon. In striatum, but not in other regions analysed, an almost 100% increase in serotonin levels and serotonin-immunoreactive fiber density was observed following 6-hydroxydopamine treatment. However, the number of serotonin-immunoreactive cell profiles in the median and dorsal raphe nuclei was not altered. The 6-hydroxydopamine treatment also led to reductions in substance P levels in striatum, nucleus accumbens and ventral mesencephalon. The cholecystokinin level in nucleus accumbens and neurotensin level in ventral mesencephalon were also reduced. A neonatal intracerebroventricular 6-hydroxydopamine treatment thus leads to a lesion of dopamine neurons in the mesencephalon with extensive loss of dopamine fibers in several forebrain areas, while localized serotonin fiber sprouting is induced in striatum. Furthermore, concomitant reductions of the levels of peptides related to the dopamine system occur following the 6-hydroxydopamine treatment. Behavioral disturbances such as hyperactivity and cognitive deficiencies occurring after a dopamine lesion early in life might therefore be due to plastic alterations in several different transmitter/neuromodulator systems as a direct or indirect consequence of the lesion.

Analysis of the O-methylated metabolites of isoprenaline, adrenaline and noradrenaline in physiological salt solutions by high-performance liquid chromatography with electrochemical detection

This study provides the first report of a sensitive, simple and rapid high-performance liquid chromatographic (HPLC) assay for the simultaneous analysis of isoprenaline and its metabolite, 3-O-methylisoprenaline, in samples of physiological salt solutions. The assay does not require time-consuming sample clean-up or extraction procedures and uses a Nova-Pak C18 column, an isocratic mobile phase and an amperometric detector. In addition, small modifications to the composition of the mobile phase have also provided sensitive assays for noradrenaline and adrenaline and their O-methylated or O-methylated deaminated metabolites (normetanephrine, metanephrine, 3-methoxy-4-hydroxyphenylethylene glycol and 3-methoxy-4-hydroxymandelic acid). These HPLC assays are sufficiently sensitive and rapid to replace the use of [3H]amines and column chromatographic separation of the metabolites for most in vitro studies on the uptake and subsequent metabolism of catecholamines by monoamine oxidase and/or catechol-O-methyltransferase in tissues.

Protection against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism by the catecholamine uptake inhibitor nomifensine: behavioral analysis in monkeys with partial striatal dopamine depletions

The neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on dopamine neurons in monkeys were found to be reduced when the catecholamine uptake inhibitor nomifensine was administered during several weeks after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The obtained protection was partial, leading to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced changes in dopamine levels to 8, 16, 52 and 59% of control values in the caudate nucleus and to 10, 16, 101 and 99% in the putamen of four animals, respectively. At the same doses, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine alone is known to deplete striatal dopamine levels to 0.5-7% of control values. Extra-nigrostriatal monoamine neurons were generally well protected by nomifensine. Neurological examinations revealed modest hypokinesia for a maximum of 10 days after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the two more severely affected animals. Reaction times of arm and eye movements were measured in a formal task in two of the monkeys having a moderate and a more important depletion of striatal dopamine, respectively. Only moderate impairments were seen during the initial 2 weeks after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in both animals. All parameters recovered to control levels thereafter. At 3.5 and 5.5 months after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, task performance was significantly better than control. The speed of arm movement remained largely unaffected during all periods of experimentation. Spontaneous eye movements were reduced in frequency and amplitude during the initial 1-2 weeks after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and recovered completely thereafter. These data suggest a substantial reduction of neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine by inhibition of catecholamine uptake. Particularly striking was the absence of major and permanent impairments in behavioral tests in which monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine alone were severely impaired. These results may warrant the development of new catecholamine uptake inhibitors for protecting nigrostriatal dopamine neurons against potential environmental toxins.

Sensitive method for determination of picogram amounts of epinephrine and other catecholamines in microdissected samples of rat brain using liquid chromatography with electrochemical detection

Liquid chromatography with high-sensitivity electrochemical detection has been employed to measure picogram amounts of epinephrine and other catecholamines in microdissected samples of the rat hypothalamus. Tissue catecholamines are purified by solvent extraction; this provides better selectivity and recovery than methods involving alumina. The solvent extraction technique has been modified in order to eliminate its major disadvantage, the presence of electroactive substances separating with catecholamines. Detection limits of below 1 pg allow for analysis of catecholamines including epinephrine in very small brain samples such as micropunches.

Norepinephrine-stimulated inositol phospholipid breakdown in the rat cerebral cortex following serotoninergic lesion

Norepinephrine (NE)-stimulated inositol phospholipid hydrolysis ("PI breakdown") in rat cerebral cortical miniprisms was used as a measure of alpha 1-adrenoceptor function following serotonin and/or NE depletion. The use of ascorbic acid to prevent autooxidation of the NE during the PI breakdown assay was found to be warranted. Treatment of rats with 5,7-dihydroxytryptamine and DSP4 produced selective depletions of serotonin (79-95%) and NE (69-85%), respectively, in cortical and hippocampal brain regions. The degree of cortical NE-stimulated PI breakdown in the lesioned animals was not significantly different from that in the control animals, suggesting that under the conditions used, serotonin and NE depletion do not lead to a changed sensitivity of alpha 1-adrenoceptors coupled to PI breakdown in the rat cortex.

Perfluorinated acids as ion-pairing agents in the determination of monoamine transmitters and some prominent metabolites in rat brain by high-performance liquid chromatography with amperometric detection

The behaviour of trifluoroacetate and heptafluorobutyrate as pairing ions for the reversed-phase ion-pair separation of monoamine transmitters and related metabolites was studied. The performance of systems with the perfluorinated acids was compared with that of systems containing sodium octyl sulphonate and was found to be better in terms of peak resolution combined with total analysis time, day-to-day reproducibility and the time required for attaining initial chromatographic equilibrium. Rat brain samples were deproteinized in the acidified mobile phase, injected directly on to a high-performance liquid chromatographic column and quantitated using an amperometric detector. Sample run times were 6-8 min, at a relatively low flow-rate. The detection limits achieved are fairly uncommon with conventional bore columns. The two perfluorinated acids studied differ in the dominant mechanisms of ion-pair formation and show selectivity differences as a result.

Acute electrophysiological and neurochemical effects of administration of MPTP in mice

The changes occurring during the first few hours after subcutaneous administration of the catecholaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were investigated. Injections of MPTP (30-60 mg/kg s.c.) reduced the impulse rate by 12-45% in all dopaminergic neurones tested in the pars compacta of the substantia nigra. Depressions were maximal at 11 min and remained present for more than 2 hr after injection. This effect was completely abolished by prior administration of the catecholamine uptake inhibitor, nomifensine (13-69 mg/kg s.c.), which prevents the toxic metabolite of MPTP 1-methyl-4-phenylpyridine (MPP+) from entering dopaminergic neurones. These results suggest an intraneuronal mechanism underlying the observed depressions in impulse rate. Levels of dopamine (DA) were decreased at 3 hr after administration of MPTP (50 mg/kg s.c.) by 60% and 54% in the striatum and substantia nigra, respectively. Pretreatment with nomifensine (25 mg/kg, intraperitoneally) prevented the decrease in DA only in the striatum. This suggests an acute DA-releasing effect of MPTP in the striatum, mediated by intracellular accumulation of MPP+, while not explaining the depression of activity of DA neurones occurring with a different time course.

Catecholamines and their metabolites

The research on biosynthesis, physiology, pharmacology, regulation and degradation of catecholamines has continuously increased for more than 50 years. This is not unexpected because of the fact that catecholamines are involved in so many life processes such as nerve conduction, blood circulation and hormone regulations in health and disease. This demands that methods for their determination should be improved, and in fact during the years a number of analytical methods have been published. About 20 years ago radioenzyme techniques with thin-layer chromatographic (TLC) separation of radiolabelled catecholamine derivatives were developed which greatly contributed to our knowledge of physiological concentrations of catecholamines in biological media, particularly in plasma and brain. Radioimmune methods were successful for analysis of a number of analytes, but for catecholamines radioimmunoassays developed slowly. We believe that the greatest potential for radioimmunochemical methods lies in their ability to localize catecholamines and metabolites at the cellular and subcellular levels. With the advent of gas chromatographic-mass spectrometric (GC-MS) and high-performance liquid chromatographic (HPLC) procedures analysis of catecholamines improved greatly., The equipment for GC-MS is expensive and requires technical skillfulness, but in experienced hands a lot of new biological data have emerged. An outstanding quality with GC-MS is that the method offers the ability to identify unknown compounds and is relatively free from interferences from extraneous compounds. In comparison with GC-MS, HPLC is versatile and has gained a widespread use. Applications for research in the catecholamine field are numerous. In general, the sensitivity and specificity are satisfactory with HPLC, but it should be borne in mind that a number of pitfalls can obscure the results. This involves both sample handling, clean-up and chromatographic procedures. At present, HPLC is the most expanding field in chromatographic determination of catecholamines and their metabolites. This is particularly the case for HPLC with electrochemical detection which has revolutionized our analytical potential in this field. These chromatographic procedures continue to develop. The prerequisites for further improved methods such as capillary zone electrophoresis and combined HPLC-MS are at hand and hopefully will soon come into more general use for analysis of catecholamines in biological samples.

Determinations of catechols in small volumes of plasma using ion-pair reversed phase liquid chromatography/electrochemistry

A method with improved sensitivity for detection of catechols (CA) in small volumes of plasma using an ion-pair reversed phase HPLC system with electromechemical detection is presented. Fast isocratic separations were obtained by using 7.5 cm x 4.6 mm (i.d.) reversed phase columns with 3C18 3 micron silica particles. The CA:s L-DOPA, Noradrenaline (NA), Adrenaline (A), Dihydroxybenzylamine (DHBA, i.s.), DOPAC and Dopamine (DA) were separated in less than 4 min. The performance of three different electrochemical cells was compared with respect to hydrodynamic voltammogram, band broadening effect, linearity and detection limit. The sample preparation procedure using alumina extraction of CA:s, was modified to improve recoveries and decrease dilution factors. A modified carbon paste cell (CP-O) gave a response 4-8 times higher than what is previously reported for GC cells. Detection limits were: L-DOPA 80, NA 1.25, A 1.25, DHBA 0.4, DOPAC 1.25 and DA 0.6 pg/injection. Application to plasma from rat and fish (cod) under rest, exercise and stress is reported. The method allows determination of CA:s in small volumes of plasma (less than 500 microliter) obtained several times a day from the same animal even if it is small (less than 1/2 kg), is under rest and parts of the plasma sample are to be used for analysis of other parameters than CA:s.

Epinephrine in mammalian brain

1. Epinephrine is widely distributed in brains of various species throughout phylogeny but maintains its localization to hypothalamus and brainstem/medulla in all species studied. 2. A general decrease in brain epinephrine content is observed phylogenetically beyond fishes with wide variation within species. 3. The cellular localization of epinephrine forming enzyme is dissociated from epinephrine stores in hypothalamus where epinephrine appears to be primarily a hormone. 4. Three proposed functional pools of epinephrine are described. Synthesis of a hormonal pool and a second, perhaps nonfunctional, pool co-stored in noradrenergic terminals in the forebrain occurs extraneuronally and is probably inhibited acutely in the presence of high corticosteroids due to inhibition of uptake 2. Synthesis of epinephrine in the neuronal pool found primarily in the medulla may be enhanced due to increased PNMT activity in the presence of elevated corticosteroids. 5. Phylogenetic and pharmacological data suggest that epinephrine may play an important role in tonic regulation of the level of arousal, reward and sensitivity to environmental stimuli in mammals.

Are there epinephrine neurons in rat brain?

The present model of epinephrine containing and PNMT containing neurons in rat brain (and by extension other species) implies that epinephrine is primarily a postsynaptic metabolite of norepinephrine in forebrain due to the probable postsynaptic localization of PNMT. As a result the most physiologically relevant pool is found in extracellular space with the bulk of tissue epinephrine found co-stored in noradrenergic terminals. Changes in the extracellular pool of epinephrine are effected by changes in the extracellular norepinephrine concentration as in times of increased release, reuptake blockade or inhibition of degradation. alpha 2-Adrenergic receptors associated with cells not necessarily in synaptic contact with the noradrenergic terminal containing epinephrine could be stimulated through this extracellular pool. The majority of PNMT containing cells in the brainstem/medulla appear to also contain other catecholamine biosynthetic enzymes. The present model suggests that epinephrine formed in these neurons is primarily used as a co-transmitter with norepinephrine formed in these same terminals. The balance of norepinephrine to epinephrine found in vesicles in these terminals would be a function of intraneuronal PNMT activity, MAO activity and reuptake which would be the major regulator of intraneuronal norepinephrine concentrations. The literature is reviewed in these contexts, questioning the existence of classical epinephrine neurons. Evidence is presented in support of a model for postsynaptic synthesis of epinephrine in the forebrain, especially during times of high norepinephrine release. The classic model of compartmentalization of biosynthetic enzymes is used in support of a co-transmitter role of epinephrine in the brainstem/medulla. Epinephrine is considered a unique metabolite of norepinephrine with important pharmacological actions and a receptor subtype in brain which monitors and regulates its formation. Epinephrine is recognized by the uptake system on noradrenergic terminals and vesicles and can therefore compete for storage in these noradrenergic neurons. Based on the distribution of PNMT and its association with major noradrenergic fiber tracts, epinephrine can be considered a site-selective metabolite of physiological and neuronal importance. Due to the compartmentalization of synthetic enzymes, it is probably not a classical neurotransmitter in the central nervous system, although it may be the primary catecholamine neurotransmitter in some medullary neurons.

Application of a novel cation-exchange reagent, Igepon T-77 (N-methyl oleoyl taurate), to microbore separations of alumina extracts of catecholamines from cerebrospinal fluid, plasma, urine and brain tissue with amperometric detection

The use of a novel amide surfactant, N-methyl oleoyl taurate (Igepon T-77), has been examined for the separation of amines on reversed-phase chromatographic material. This reagent was found to partition onto the C18 material in a partially irreversible and concentration independent manner. When the stationary phase is saturated with this surfactant, the loaded column performs as a strong cation exchanger. Novel separations are possible as a result of secondary hydrogen-bonding effects which modify classical retention order for primary, secondary and tertiary amines. Sensitive and selective applications of these separations are demonstrated for catecholamine determinations in blood plasma, cerebrospinal fluid, urine and brain tissue. Additional sensitivity is obtained for epinephrine by taking advantage of the pH-dependent intramolecular cyclization and on-column concentration of large injection volumes.

Determination of monoamines by use of liquid chromatography with electrochemical detection in the study of selective monoamine neurotoxins

Determination of regional monoamine levels in the CNS in the study of the effects of selective monoaminergic neurotoxins is a reliable method with which to study the morphological changes in denervated as well as re- or hyperinnervated regions as evidenced by comparisons with several other methods. In the acute stage, the changes in monoamine levels reflect both the beginning of the degeneration and the acute pharmacological effects exerted by several monoaminergic neurotoxins. The only exception to this seems to be the MPTP-induced chronic decrease of DA in the nucleus accumbens and the tuberculum olfactorium where no morphologic changes have been found so far.

Simultaneous liquid chromatographic determination of seventeen of the major monoamine neurotransmitters, precursors and metabolites. II. Assessment of human brain and cerebrospinal fluid concentrations

The optimized chromatographic method procedure presented in Part I was employed for the assessment of human brain and cerebrospinal fluid neurotransmitters levels. The optimized sample preparation and chromatographic conditions permitted a rapid (less than 25 min), sensitive and semi-automated high-performance liquid chromatographic analysis which measures all major monoamine neurotransmitters, precursors and metabolites in human brain and cerebrospinal fluid. The brain specimen was deproteinized with perchloric acid (containing Na2EDTA and sodium sulphite), the internal standard and heparin were added and the samples were sonicated, centrifuged, filtered and injected directly into the chromatographic system. Cerebrospinal fluid was handled in a similar manner except that sonication was excluded. The regional distribution of monoamine neurotransmitter concentrations in human brain and cerebrospinal fluid is presented.

Studies on the effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on central catecholamine neurons in C57BL/6 mice. Comparison with three other strains of mice

The effect of the parkinsonism-inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on central catecholamine neurons in C57BL/6 mice has been studied employing neuro- and histochemical techniques. The number of dopamine (DA) cell bodies in substantia nigra pars compacta (SNC) was reduced by 70% in MPTP-treated C57BL/6 mice, as demonstrated both by tyrosine hydroxylase (TH) immunohistochemistry and conventional histology (Cresyl violet staining) and an almost complete loss of DA fibers in striatum was also found. A detailed analysis of the effects of MPTP on endogenous catecholamine levels in various brain regions revealed that MPTP caused a severe reduction of endogenous DA in substantia nigra and striatum (35 and 5% of control) which was accompanied by an increase in the 3,4-dihydroxyphenylacetic acid (DOPAC)/DA ratio. There was also a decrease of DA in nucleus accumbens and the olfactory tubercle to 41 and 44% of control, respectively, without any significant change in the DOPAC/DA ratio and density of TH-positive fibers. Small but significant decreases of the noradrenaline (NA) levels in septum, entorhinal cortex and frontal cortex were seen, although the uptake of [3H]NA in frontal cortex was not significantly changed. Minor MPTP-induced decreases of the serotonin levels in frontal cortex, occipital cortex and spinal cord were also seen. The MPTP treatment also induced a 55% increase of adrenaline levels in hypothalamus, while no changes were seen in pons-medulla and spinal cord. Comparing this with 3 other strains of mice, the MPTP-induced reduction of endogenous DA in striatum was most pronounced in C57BL/6, less in N.M.R.I. and CBA/Ca mice, and least in Swiss-Webster. Concerning the effect of MPTP on cortical NA levels, the same relation was at hand except for C57BL/6, where, as mentioned, the effect was merely detectable. No reduction of DA perikarya in SNC was seen in Swiss-Webster mice. These findings show that in mice major differences exist in sensitivity of catecholamine neurons to MPTP between different strains. The data show that MPTP can produce an almost complete, permanent and relatively selective degeneration of the nigrostriatal DA neurons in C57BL/6 mice similar to that seen in primates. This strain may therefore serve as a useful model for studies on various aspects of MPTP-induced parkinsonism.

Effect of sample preparation and liquid chromatography column choice on selectivity and precision of plasma catecholamine determination

Research into the role of the catecholamines has often depended on the reliable determination of plasma catecholamine concentrations, which present a challenge since they are normally in the low pg/ml range. Most methods employ liquid chromatography, with variations in sample preparation, the separation mechanism, and detection. We tested a new approach to sample clean-up using boric acid gel instead of alumina. No advantage was found. We also compared cation-exchange separation with ion-pair chromatography. Several improvements are possible with the former, most notably greater precision, better specificity, and increased throughput.

Abundance in the embryonic brainstem of adrenaline during the absence of detectable tyrosine hydroxylase activity

The activities of the catecholamine synthetic enzymes tyrosine hydroxylase and phenylethanolamine N-methyltransferase, and the concentrations of the catecholamines and their respective metabolites, have been measured in the dorsal and ventral halves of the brainstem at various ages in the embryonic and adult rat. The activity of phenylethanolamine N-methyltransferase in both parts of the brainstem at day 14 of gestation is at or greater than adult levels and thereafter displays relatively small variations during ontogeny. Tyrosine hydroxylase activity, in contrast, is undetectable at day 14 and increases slowly, achieving only 20-25% of adult values by day 18 of gestation. Adrenaline concentrations correlate well with the activity of phenylethanolamine N-methyltransferase, showing a precocious development, whereas noradrenaline and 3,4-dihydroxyphenylethylamine (dopamine) concentrations are more closely related to the enhancement of tyrosine hydroxylase activity; at day 18 of gestation, for example, they are only 5 and 10%, respectively, of the adult values. The concentrations of the metabolites of noradrenaline and dopamine are suggestive of a high rate of turnover. These results confirm previous immunocytochemical evidence of a tardy appearance of tyrosine hydroxylase-like immunoreactivity in the phenylethanolamine N-methyltransferase-positive perikarya of the embryonic medulla oblongata. In addition, the abundance of adrenaline in this area at early gestational stages strongly suggests that, despite the paucity of tyrosine hydroxylase, phenylethanolamine N-methyltransferase is active in vivo and is utilizing a substrate other than noradrenaline. It is likely, however, that at later stages of gestation, when tyrosine hydroxylase is present at sufficient activity to supply noradrenaline, the conventional synthetic pathway for adrenaline formation comes into being.

Uptake inhibition protects nigro-striatal dopamine neurons from the neurotoxicity of 1-methyl-4-phenylpyridine (MPP+) in mice

Intracerebroventricular administration of MPP+ to C57 BL/6 mice caused a pronounced depletion of striatal levels of dopamine and 3,4-dihydroxyphenyl-acetic acid ipsilaterally, and a less marked depletion contralaterally. The MPP+-induced reductions were clearly diminished by pretreatment with the dopamine uptake inhibitors mazindol and nomifensine. Similar results were obtained from determinations using tyrosine hydroxylase immunohistochemistry. These results are consistent with the hypothesis that MPTP neurotoxicity is related to the formation of MPP+ from MPTP outside the dopamine neurons and that subsequent uptake of MPP+ into these neurons initiates degeneration.

Selective lesioning of forebrain noradrenaline neurons at birth abolishes the improved maze learning performance induced by rearing in complex environment

The effect of selective destruction of forebrain noradrenaline (NA) neurons induced by 6-hydroxydopamine (6-OHDA) at Day 1 after birth on Hebb-Williams maze performance was investigated in adult rats housed after weaning in a complex environment (EC) or an isolated (IC) environment for 35 days. Saline treated control rats raised in the EC made fewer errors than those raised in the IC. This effect of EC was completely abolished in 6-OHDA treated rats; for these animals no improved performance due to the housing condition was obtained. Protection of the NA neurons against 6-OHDA neurotoxicity by pretreatment with desipramine (DMI) resulted in an effect of EC identical to that seen in saline-treated controls. Postweaning housing in the IC led to an increased locomotion as compared to housing in EC, but this effect was not affected by neonatal 6-OHDA and/or DMI treatment. Neurochemical analysis confirmed cortical NA and metabolite depletion as well as a good protection by the DMI pretreatment. The present results indicate that central NA neurons are involved critically in mediating mainly the cognitive components of behavioral alterations induced by EC.

Central and peripheral changes in catecholamine-synthesizing enzyme activities after systemic administration of the neurotoxin DSP-4

In brain regions containing noradrenergic (NA) cell bodies or terminals, DSP-4 induces changes in the activity of catecholamine-synthesizing enzymes which suggest that central NA neurons are lesioned by this neurotoxin. In contrast, the lack of change in the same enzymatic activities in an area containing mostly adrenergic (A) neurons (C2 region), favors the hypothesis of a resistance of the A neurons to DSP-4. Furthermore, the enzymatic changes observed in peripheral organs suggest a peripheral activation of the NA cell bodies in response to lesioning of the sympathetic terminals by DSP-4.

Impaired selective attention in methylazoxymethanol-induced microencephalic rats

Prenatal treatment of rats on gestation day 15 with methylazoxymethanol (MAM) caused forebrain microencephaly. Several behavioral tests were performed when the rats had reached an adult age. MAM treated rats were hyperactive, and were severely impaired in the acquisition of successive position reversal in a T-maze. The microencephalic rats failed also to demonstrate contextual control of latent inhibition (the stimulus preexposure effect) in taste-aversion conditioning. These results indicate that MAM treatment disrupts attentional processes and that this may account for the learning impairment.