Reproducibility of the measurement of plasma noradrenergic and dopaminergic metabolites in normal subjects

Norepinephrine and impulsivity: effects of acute yohimbine

RATIONALE

Rapid-response impulsivity, characterized by inability to withhold response to a stimulus until it is adequately appraised, is associated with risky behavior and may be increased in a state-dependent manner by norepinephrine.

OBJECTIVE

We assessed effects of yohimbine, which increases norepinephrine release by blocking alpha-2 noradrenergic receptors, on plasma catecholamine metabolites, blood pressure, subjective symptoms, and laboratory-measured rapid-response impulsivity.

METHODS

Subjects were 23 healthy controls recruited from the community, with normal physical examination and ECG, and negative history for hypertension, cardiovascular illness, and axis I or II disorder. Blood pressure, pulse, and behavioral measures were obtained before and periodically after 0.4 mg/kg oral yohimbine or placebo in a randomized, counterbalanced design. Metabolites of norepinephrine [3-methoxy-4-hydroxyphenylglycol (MHPG) and vanillylmandelic acid (VMA)] and dopamine [homovanillic acid (HVA)] were measured by high-pressure liquid chromatography with electrochemical detection. Rapid-response impulsivity was measured by commission errors and reaction times on the immediate memory task (IMT), a continuous performance test designed to measure impulsivity and attention.

RESULTS

Yohimbine increased plasma MHPG and VMA but not HVA. Yohimbine increased systolic and diastolic blood pressure and pulse rate. On the IMT, yohimbine increased impulsive errors and impulsive response bias and accelerated reaction times. Yohimbine-associated increase in plasma MHPG correlated with increased impulsive response rates. Time courses varied; effects on blood pressure generally preceded those on metabolites and test performance.

CONCLUSIONS

These effects are consistent with increased rapid-response impulsivity after pharmacological noradrenergic stimulation in healthy controls. Labile noradrenergic responses, or increased sensitivity to norepinephrine, may increase risk for impulsive behavior.

Variability of plasma homovanillic acid over 13 months in patients with schizophrenia; relationship with the clinical response and the Wisconsin card sort test

In the present study we have measured, on a monthly basis, the concentration of plasma homovanillic acid (pHVA) in schizophrenic patients during 13 months of their pharmacological treatment. The average pHVA values of each patient were within the range of 7.30-17.70 ng/ml and the coefficients of variation for each patient (CV %) were within the range of 13-33%. Half of the patients that showed higher pHVA CV% values also showed higher scores on the Brief Psychiatric Rating Scale at the beginning of the study, and improved more after 6 months, when compared to the remaining 50% with lower CV% values. There was no significant relationship between the scores of the Wisconsin Card Sort Test and the concentration or the CV% of the pHVA of each patient. A greater variability in the pHVA may be associated with a greater plasticity of the dopaminergic system and a better clinical response.

Inter- and intra-individual variability in the levels of plasma homovanillic acid in schizophrenic patients

BACKGROUND

Changes in the levels of homovanillic acid in blood plasma (pHVA) may reflect changes which occur in the brain. In healthy individuals, this concentration of pHVA is stable over time.

METHODS

Over the course of one month, we studied 98 acute schizophrenic patients who had not been taking any medication but were administered neuroleptics upon hospital admission, together with 23 chronic schizophrenic patients on long-term treatment from whom medication was withdrawn. Blood samples were taken at regular intervals from each individual and the concentration of plasma homovanillic acid was measured.

RESULTS

We found relative stable values of pHVA with an intraclass correlation coefficient of 0.363 in acute patients and 0.638 (p<0.0001) in chronic patients, although no differences were found in mean values (13.79 and 14.18 microg/L, respectively) or in the variation range (7.20 to 26.7 microg/L and 6.96 to 29.96 microg/L respectively). The index of individuality was calculated to be 1.36 in acute patients and 0.74 in chronic patients.

CONCLUSIONS

Despite the wide range of values in the concentration of pHVA and the presence of pharmacological stimuli, we found a certain reproducibility in the levels of this dopamine metabolite. These findings are consistent with the idea that the dopaminergic activity is characterized by a constitutive value which would be under genetic control. The higher stability observed in chronic patients may reflect a weaker, age-related dopaminergic plasticity; conversely, it may indicate that a lack of plasticity in response to a pharmacological stimulus may be an indicator of poorer prognosis.

Reproducibility of plasma catecholamine metabolites in normal subjects

BACKGROUND

Plasma homovanillic acid (HVA) and methoxy-hydroxy-phenylglycol (MHPG) are often used in repeated measurement designs to assess dopamine and norepinephrine metabolism in clinical research. However, only limited data on the reproducibility of these metabolites are currently available.

METHODS

Plasma HVA and MHPG were measured in normal volunteers on five nonconsecutive mornings under fasting conditions and restricted smoking and physical activity.

RESULTS

Intraclass correlation coefficients (ICC) for plasma HVA and MHPG across 5 days were determined to be 0.85 and 0.79, respectively. ICC improved to 0.90 for HVA and 0.91 for MHPG when the average of the first 2 days was examined against the average of the last 2 days.

CONCLUSIONS

Results suggested that under controlled conditions plasma HVA and MHPG measurements have good reproducibility.

Plasma vanillylmandelic acid level as an index of psychological stress response in normal subjects

The relationships between psychological stress responses and plasma levels of vanillylmandelic acid (VMA), 3-methoxy-4-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 5-hydroxyindolacetic acid (5-HIAA) were investigated in normal volunteers. Two questionnaires were used to measure stress: the Psychological Stress Response Scale (PSRS) and the State-Trait Anxiety Inventory (STAI). Plasma levels of VMA--but not MHPG, HVA, and 5-HIAA--showed significant positive correlations with PSRS emotional and cognitive-behavioral stress and STAI state anxiety. Significant positive correlations were also found between plasma levels of VMA and MHPG and psychological stress responses measured repeatedly in a longitudinal study of an Olympic swimmer. Plasma VMA measurements, which reflect the level of activity of the peripheral sympathetic nervous system, may provide a useful biochemical index of psychological stress responses in normal subjects.

Homovanillic acid and dopamine-beta-hydroxylase in male youth: relationships with paternal substance abuse and antisocial behavior

Recent research suggests that dopaminergic/noradrenergic system dysfunction may be associated with substance abuse and/or antisocial behavior. In order to determine whether male youth of fathers with these disorders would manifest differences in these systems when compared with youth of nonsubstance-abusing or nonantisocial fathers, levels of homovanillic acid (HVA), the metabolite of dopamine (DA) and dopamine-beta-hydroxylase (DBH), the enzyme facilitating the conversion of dopamine to norepineprhine, were studied in offspring blood samples. The subjects were 65 male youth aged 6-15 years admitted to a residential center because of behavioral disorders. Parental substance abuse and antisocial behavior were assessed through interviews, rating scales, and/or chart review. HVA and DBH were determined from blood samples obtained after admission. The findings indicated that youth of substance-abusing fathers had significantly greater levels of HVA than yough of nonsubstance-abusing fathers. Younger (< 12.0 years) boys of antisocial fathers had significantly lower DBH activity than comparably aged youth of nonantisocial fathers. The results suggest that common generational links in substance abuse and antisocial behavior in males may be associated with detectable biological parameters in susceptible youth.

The use of the rat iris as a model system to evaluate the effect of the cholinotoxin, AF64A, in vivo

The iris is innervated by both cholinergic parasympathetic, and adrenergic sympathetic branches of the autonomic nervous system. This innervation represents a simple and anatomically well-defined system to evaluate the effects of chemical compounds on cholinergic and adrenergic neurons. AF64A (acetyl ethylcholine aziridinium) is a known cholinotoxin in the brain and, in these experiments using the iris system, we evaluated its in vivo effect on cholinergic enzyme activity, pupillary size, and catecholamine neurotransmitter levels. We found in this system that AF64A reduces the activity of choline acetyltransferase (ChAT) but not acetylcholinesterase (AChE). AF64A is selective for cholinergic neurons, since norepinephrine and dopamine levels were unaffected.

Auditory sensory gating, hippocampal volume, and catecholamine metabolism in schizophrenics and their siblings

Schizophrenia may result from the concerted action of several pathophysiological factors. This pilot study compared the distribution of measurements of three such putative factors in 11 schizophrenics and their siblings: a neurophysiological deficit in auditory sensory gating, diminished hippocampal volume, and increased catecholamine metabolism. Abnormal auditory sensory gating was found in all schizophrenics in the 11 families studied and in 8 of their 20 siblings. Compared with the schizophrenics, the clinically unaffected siblings with abnormal auditory gating had larger hippocampal volume. There was no similar difference for the siblings with normal gating. The siblings with abnormal auditory gating also had lower homovanillic acid levels than the other siblings. The data suggest that a familial neuronal deficit, identified by diminished sensory gating, may be a necessary, but not sufficient factor in the pathogenesis of schizophrenia. Individuals with this deficit are generally clinically unaffected, except for schizophrenics, who also have other abnormalities, such as diminished hippocampal volume and increased catecholamine metabolism.

Sensation seeking in psychiatrically disturbed youth: relationship to biochemical parameters and behavior problems

OBJECTIVE

Relatively little research has been conducted on the relationship of personality traits or behavioral tendencies with biological parameters in youth. This study was intended to determine whether relationships exist between self-reported sensation-seeking tendencies and biochemical parameters in boys.

METHOD

Twenty-five male youth aged 8 to 15 years admitted to a residential diagnostic center because of noncompliant, disruptive, and/or antisocial behavior were studied. Biochemical parameters associated with sensation seeking in adults or antisocial behavior were measured along with diagnoses, behavior ratings, and self-reported sensation seeking.

RESULTS

High sensation seeking, as assessed on a newly developed sensation-seeking scale for children, was inversely correlated with 3-methoxy-4-hydroxyphenylglycol (MHPG) levels in the older youth (> or = 12.0 years) but not in the younger boys (< 12.0 years) in the group. Elevations on the sensation seeking scale also correlated marginally in these older youth with parent-reported problems on a behavior rating scale, reflecting "delinquent" behavioral tendencies.

CONCLUSIONS

The findings support hypothesized noradrenergic dysregulation in some sensation-seeking persons (including youth > or = 12.0 years) and the relationship between high sensation-seeking tendencies and antisocial or disruptive behavioral disorder.

Acidic and basic fibroblast growth factor mRNAs are increased in striatum following MPTP-induced dopamine neurofiber lesion: assay by quantitative PCR

Acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF), the two best characterized members of a growing family of heparin-binding growth factors, have been shown to affect both survival of cultured neurons and regeneration of nerve terminals when applied exogenously. The endogenous expression of these growth factors in response to brain injury is not well understood. We have utilized the Swiss-Webster mouse, treated with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and a quantitative polymerase chain reaction assay to examine changes in endogenous synthesis of mRNA for both aFGF and bFGF in the striatum and substantia nigra. We have found that MPTP treatment results in a loss of 95% of dopaminergic function and is accompanied by an increase in expression of both aFGF and bFGF in the striatum at 1 week post-lesion. After 5 weeks, the terminals appear to be regenerating and FGF mRNA expression has returned to control levels. These results suggest that cellular reaction to chemical lesion in the brain may involve changes in growth factor expression, including both aFGF and bFGF.

Auditory sensory gating and catecholamine metabolism in schizophrenic and normal subjects

Diminished neuronal response to repeated sensory input is a sensory-gating phenomenon that has been found to be deficient in schizophrenic patients. For example, schizophrenic patients fail to decrease the amplitude of the P50 wave of the auditory evoked potential to the second of paired click stimuli. In some studies, however, normal subjects have also failed to decrease their P50 responses. The aim of this study was to determine if accommodation to the recording situation over time would affect the gating of the P50 response. The gating of the P50 wave is measured as the ratio of the amplitude of the second response to the amplitude of the first. Three successive auditory evoked potentials were compiled, each from trains of 32 pairs of stimuli. Twelve normal subjects and 12 schizophrenic patients were studied. Unconjugated catecholamine metabolites were measured from venous samples drawn before and after the electrophysiological recording. Between the first and third trials, the normal subjects significantly increased their gating of P50. This increase in gating of P50 was related to decreased levels of the noradrenergic metabolite 3-methoxy-4-hydroxyphenylglycol. No similar phenomenon was observed in the schizophrenic patients, a number of whom had a further decrease in P50 gating over the three trials. Transient failure to observe gating of P50 in normal subjects may be related to increased state-dependent noradrenergic activity, which is known to disrupt sensory gating. This mechanism does not seem to account for the more persistent failure of sensory gating in schizophrenia.

Plasma amine oxidase activities in Norrie disease patients with an X-chromosomal deletion affecting monoamine oxidase

Two individuals with an X-chromosomal deletion were recently found to lack the genes encoding monoamine oxidase type A (MAO-A) and MAO-B. This abnormality was associated with almost total (90%) reductions in the oxidatively deaminated urinary metabolites of the MAO-A substrate, norepinephrine, and with marked (100-fold) increases in an MAO-B substrate, phenylethylamine, confirming systemic functional consequences of the genetic enzyme deficiency. However, urinary concentrations of the deaminated metabolites of dopamine and serotonin (5-HT) were essentially normal. To investigate other deaminating systems besides MAO-A and MAO-B that might produce these metabolites of dopamine and 5-HT, we examined plasma amine oxidase (AO) activity in these two patients and two additional patients with the same X-chromosomal deletion. Normal plasma AO activity was found in all four Norrie disease-deletion patients, in four patients with classic Norrie disease without a chromosomal deletion, and in family members of patients from both groups. Marked plasma amine metabolite abnormalities and essentially absent platelet MAO-B activity were found in all four Norrie disease-deletion patients, but in none of the other subjects in the two comparison groups. These results indicate that plasma AO is encoded by gene(s) independent of those for MAO-A and MAO-B, and raise the possibility that plasma AO, and perhaps the closely related tissue AO, benzylamine oxidase, as well as other atypical AOs or MAOs encoded independently from MAO-A and MAO-B may contribute to the oxidative deamination of dopamine and 5-HT in humans.

The effect of age, sex, weight and height on the plasma concentrations in healthy subjects of the acidic metabolites of some biogenic monoamines involved in psychiatric and neurological disorders

1. The plasma concentrations of unconjugated phenylacetic acid and m-hydroxyphenylacetic acid are lower in male than in female subjects. 2. The plasma concentrations of unconjugated phenylacetic acid and mandelic acid decrease with increasing weight and height for all subjects combined. The same relationships apply for both males and females but are significant only for males. 3. Homovanillic and vanillylmandelic acid concentrations in plasma increase with age. 4. The importance of using age, sex, weight and height matched groups in studies involving the plasma concentrations of some of the trace amine metabolites in psychiatric disorders has been demonstrated. This is particularly the case for phenylacetic acid, the major metabolite of phenylethylamine which is now thought to be a neuromodulator of catecholaminergic neurotransmission.

Sensory gating deficits in psychiatric inpatients: relation to catecholamine metabolites in different diagnostic groups

Acutely ill psychiatric inpatients were examined for a deficit in sensory gating, measured as failure to suppress the P50 wave of the auditory-evoked response to the second of paired stimuli. Previously, we had found that in mania, this sensory gating deficit is correlated with increased plasma-free levels of the noradrenergic metabolite 3-methoxy, 4-hydroxyphenylglycol (pMHPG), whereas in schizophrenia, there is no correlation with catecholamine metabolism. To assess the generalizability of these findings, we examined inpatients with a broader range of diagnoses, including those with multiple DSM III-R Axis I, II, and III diagnoses. The patients were grouped into three diagnostic spectra for analysis: schizophrenic, manic, and depressive. In the schizophrenic patients, there was no relationship between pMHPG or other catecholamine metabolites and the sensory gating deficit. In manic patients, however, a positive correlation between pMHPG level and the sensory gating deficit was again observed. This relationship did not extend to the depressive patients, who uniquely showed sensory gating deficits that correlated negatively with the severity of their illness. The data suggest that sensory gating deficits are common to these three diagnostic spectra, but the deficits in each group have different relationships to catecholamine metabolism and symptom severity that may reflect differences in the underlying neuronal pathophysiology of these illnesses.

Sensory physiology and catecholamines in schizophrenia and mania

Hypersensitivity to sensory stimulation is a prominent characteristic of both schizophrenia and mania. Neurophysiological recordings suggest a common deficit in a central neuronal sensory gating mechanism which regulates sensitivity to repeated auditory stimuli. Dopamine and norepinephrine are hypothesized to have major roles in these illnesses, but their role in aberrant sensory processing has not yet been proved. Presumptive evidence for effects of catecholamines on sensory processing comes from psychophysiological studies of normal subjects challenged with stimulants who show decreased sensory gating, and studies of psychotic patients treated with neuroleptics who show improved function. Studies of similar phenomena in animals show comparable effects of catecholamines on sensory processing, both behaviorally and at the single neuron level. In this study, gating of auditory evoked potentials (EPs) during treatment of both illnesses was compared with plasma dopamine and norepinephrine metabolites. Comparisons of medicated and unmedicated states showed that schizophrenic patients have a fixed deficit in sensory gating, which is a familial trait, unchanged by medication. During acute illness, they have an additional transient hypersensitivity to stimuli, manifested as smaller EPs, which seems to be mediated by dopamine. Manic patients have only the deficit in sensory gating, which is transient and seems to be mediated by norepinephrine. Thus, similar neurophysiological deficits in the two psychoses are associated with different biochemical abnormalities, which may explain similarities in acute symptoms and differences in other aspects of the illnesses, such as their response to treatment.

Unconjugated methoxylated catecholamine metabolites in human saliva. Quantitation methodology and comparison with plasma levels

A newly developed method for the simultaneous extraction and quantitation of the unconjugated levels of the catecholamine metabolites vanilmandelic acid (VMA), 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) and homovanillic acid (HVA) in plasma by high performance liquid chromatography with electrochemical detection was modified and applied to studies of human saliva. The assay had a mean coefficient of variation under 3% for each of the metabolites. Levels of plasma VMA, MHPG and HVA were measured in 28 normal subjects and compared to their saliva levels, obtained before and after stimulation by mastication. Significant correlations were found between plasma and saliva MHPG and HVA, but there was no correlation between plasma and saliva VMA. Salivary MHPG and HVA can be reproducibly assayed and may be useful tools for indications of changes in central and peripheral catecholamine metabolism.

Eye movements in cocaine abusers

Using electro-oculography, we quantitatively investigated eye movements in nine heavy cocaine abusers and three groups of controls. Plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG), a major metabolite of brain norepinephrine, in cocaine abusers were reduced to an average of 53% of normal. Cocaine abusers had normal smooth pursuit, optokinetic nystagmus, vestibulo-ocular reflex, visual suppression of the vestibulo-ocular reflex, and caloric nystagmus. Data were suggestive of a significant reduction in the degree of immediate enhancement of visual-vestibulo-ocular reflex gain by magnified vision in the cocaine abusers. However, adaptive plasticity of the vestibulo-ocular reflex was normal in the cocaine abusers. These results suggest that, despite animal data linking vestibulo-ocular reflex plasticity to central norepinephrine, this neurotransmitter may not be important to plasticity in human beings.

Direct determination of unconjugated HVA in human plasma filtrates by HPLC coupled with dual-electrode coulometric electrochemical detection

We report a procedure for the rapid determination of unconjugated homovanillic acid (HVA) in human plasma by cartridge filtration followed by direct injection into an isocratic HPLC system coupled with dual-electrode coulometric electrochemical detection. Sample preparation is rapid and more than 72 samples can be studied in 24 h using an automated HPLC system. The intra- and interassay precisions of the assay equal or exceed previously reported methods. While this methodology has been employed to study plasma free HVA, the concept of the technique may be applicable to other compounds, as well as different assay procedures, to greatly decrease sample preparation time.

Plasma amine metabolites before and after withdrawal from neuroleptic treatment in chronic schizophrenic inpatients

Plasma catecholamine metabolites were measured in paired blood samples from 22 subjects with chronic schizophrenia. One sample was drawn while patients were on a stable dose of neuroleptic medication; the second was drawn 6 weeks after discontinuation of medication. In comparison with baseline values during neuroleptic treatment, there was a significant increase in the plasma concentration of the norepinephrine metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), and a trend toward an increase in the plasma concentration of the dopamine metabolite, homovanillic acid (HVA), in the medication-free subjects. There were no significant correlations between plasma MHPG or HVA concentrations and the corresponding ratings of psychopathology for these patients.