Origin of free 3-methoxy-4-hydroxyphenylethyleneglycol

The relationship between plasma MHPG and NE: employing regression models in estimating centrally derived MHPG and peripheral NE turnover rate in panic disorder

Studies investigating the role of the noradrenergic system in the pathophysiology of anxiety have focused on measuring plasma 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) levels. Fewer studies have examined norepinephrine levels. Basal plasma norepinephrine and free MHPG levels were simultaneously measured in 33 normal controls and 20 panic disorder (PD) patients. Norepinephrine levels were similar in patients and controls, but MHPG levels were significantly lower in patients (13.34 +/- 3.22 vs 18.37 +/- 4.49 pmol ml-1, p < 0.0001). Norepinephrine correlated significantly with plasma MHPG levels in controls (r = 0.538, p < 0.0001) and patients (r = 0.645, p < 0.002). Patients had a trend toward a lower y-intercept than controls, suggesting a lower contribution by the CNS to MHPG pool plasma levels (9.18 vs 12.51, p < 0.08). Norepinephrine turnover rate was similar in patients and controls. We propose that the dysregulation in the noradrenergic system in PD may be akin to animal studies of acute-on-top-of-chronic stress paradigms, whereby chronic stress results in normal or decreased basal NE turnover and sensitized responses to recurrent stresses.

Loss of intraventricular fluid melatonin can explain the neuropathology of Alzheimer's disease

Loss of intraventricular fluid melatonin explains why Alzheimer's disease neuropathology has a laminar, regional and neural-system-specific pattern, which includes the entorhinal cortex, CA1 of the hippocampus, the dorsal raphe nucleus and the locus ceruleus. High metabolic activity may be part of the neuronal vulnerability. Without elevated levels of ventricular fluid melatonin, the hydroxyl radical damages the mitochondria of the most active neurons, causing apoptosis, with resultant failure of the memory system. General brain atrophy follows in the absence of new memory formation.

Concentration gradients for monoamine metabolites in lumbar cerebrospinal fluid

Concentration gradients in lumbar cerebrospinal fluid (CSF) for the monoamine metabolites homovanillic acid (HVA), 5-hydroxy-indoleacetic acid (5-HIAA) and 4-hydroxy-3-methoxyphenylglycol (HMPG) were studied in 9 healthy controls and 47 neuropsychiatric patients without diseases causing disturbed CSF circulation. In a serial sampling of the first 24 ml of CSF, steep concentration gradients between the first (0-4th ml) and last (21st-24th ml) portions of CSF were found for HVA (99 +/- 59% increase; p < 0.001) and 5-HIAA (88 +/- 54% increase; p < 0.001), while the concentration gradient was slight for HMPG (11 +/- 7% increase; p < 0.001). The existence of marked concentration gradients for the monoamine metabolites HVA and 5-HIAA gives further evidence for an active transport system for these metabolites and indicates that the lumbar CSF-HVA and 5-HIAA levels reflect the dopamine and serotonin metabolism in the brain. Moreover, the existence of pronounced concentration gradients for HVA and 5-HIAA stresses the importance of making analyses on a standardized volume of CSF.

Catecholamine metabolism during additional administration of DL-threo-3,4-dihydroxyphenylserine to patients with Parkinson's disease

DL-threo-3,4-dihydroxyphenylserine (DL-threo-DOPS) was administered during 10 days to 4 patients with longstanding Parkinson's disease in addition to their treatment with L-3,4-dihydroxyphenyl-L-alanine (L-DOPA)-carbidopa (Sinemet). All patients tended to improve in their symptoms freezing, all day life activity and mood. There were no improvements in rigidity, tremor, and akinesia (in general). During the DL-threo-DOPS-treatment cerebrospinal fluid (CSF), serum and urine concentrations of catecholamines were measured. The results show that DL-threo-DOPS is transported to the brain and CSF in a way comparable with L-DOPA. However, no measurable increase of 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG) in CSF could be demonstrated. This suggests that the synthesis of noradrenaline from DL-threo-DOPS in the brain is doubtful. In addition measurements in urine reveals that at the dose used Sinemet prevents peripheral decarboxylation of DL-threo-DOPS into noradrenaline. Other possible metabolic pathways of DL-threo-DOPS are discussed.

Comparison of free MHPG in rat cerebrospinal fluid with free and conjugated MHPG in brain tissue: effects of drugs modifying noradrenergic transmission

The changes of free 3-methoxy-4-hydroxyphenylglycol (MHPG) in cerebrospinal fluid (CSF) were compared with the corresponding alterations of free and conjugated MHPG in rat brain tissue after various pharmacological treatments modifying noradrenergic neurotransmission. In addition, the effects of the drug treatments on the concentration of noradrenaline (NA) in brain were determined. alpha-Methyl-p-tyrosine (an inhibitor of tyrosine hydroxylase) induced decreases in free and conjugated MHPG in CSF and brain; the free species appeared to decline more rapidly. Reserpine caused similar biphasic changes in free MHPG in CSF and brain but the rapid and transient initial increase in MHPG-SO4 was very weak. Pargyline (monoamine oxidase inhibitor) induced a sharp decline in the concentration of free MHPG in brain and CSF while MHPG-SO4 in brain definitely decreased more slowly. Relatively similar time courses were seen for all three MHPG parameters after administration of MPV-1248 (alpha 2-antagonist) and clonidine (alpha 2-agonist) i.e., increases and decreases, respectively. The present results support the validity of monitoring drug-induced acute changes in central turnover of NA by repeated measurements of free MHPG levels in rat cisternal CSF.

alpha 2-Adrenoceptor agonists decrease free 3-methoxy-4-hydroxyphenylglycol in rat cerebrospinal fluid

The effects of alpha 2-adrenoceptor agonists on the concentrations of monoamine metabolites in cisternal cerebrospinal fluid (CSF) of freely moving rats were determined. Clonidine and two new imidazole derivatives, detomidine and medetomidine, and diazepam (as a control substance) were administered in sedative doses and the concentrations of unconjugated 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in CSF were monitored for 48 h. The alpha 2-agonists caused a dose-dependent, statistically significant decrease in the concentration of MHPG in CSF compared to the concentration in animals treated with saline or diazepam. Detomidine caused a statistically significant increase in the concentration of 5-HIAA compared to control treatments. The present results demonstrate the usefulness of monitoring drug-induced alterations in central nervous system (CNS) noradrenergic activity by measuring free MHPG in repeatedly collected cisternal CSF samples from freely moving rats. The alpha 2-agonists reduced the concentration of MHPG in CSF, indicating a decreased release, metabolism and turnover of noradrenaline in the CNS.

Clonidine and cortical plasticity: possible evidence for noradrenergic involvement

In order to test the hypothesis that noradrenergic transmission modulates ocular dominance plasticity in kitten visual cortex, we monocularly deprived kittens while administering the alpha-2 adrenergic agonist clonidine (CLON). To avoid bias in testing the hypothesis, we included, with a single blind technique, saline-treated control kittens in the series. First, using high-pressure liquid chromatography, we demonstrated that CLON treatments resulted in an average decline in cerebrospinal fluid levels of the norepinephrine metabolite, 3-methoxy-4-hydroxy phenylethylene glyolol (MHPG) of 44%. Then, single-unit recording in area 17 revealed the expected ocular dominance (OD) shift in monocularly deprived saline controls, but recording failed to find a significant shift in CLON-treated kittens. Our results support the notion that CLON treatment interferes with ocular dominance plasticity by inhibiting noradrenergic transmission in visual cortex. We discuss side effects of CLON, concluding that CLON's sedative effect may contribute to the lack of OD shift.

Repetitive measurement of monoamine metabolite levels in cerebrospinal fluid of conscious rats: effects of reserpine and haloperidol

A simple high performance liquid chromatographic method with electrochemical detection is described for the simultaneous determination of unconjugated 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA), the principal central nervous system (CNS) metabolites of noradrenaline, serotonin and dopamine (DA), respectively, in small samples of cisternal cerebrospinal fluid (CSF) obtained repeatedly from freely moving rats. Amounts of 30-50 microliter of CSF could be collected repeatedly every 30-60 min allowing monitoring of monoamine metabolite concentration levels in CSF under physiological conditions. None of the metabolites showed any clear diurnal variation. A single injection of reserpine caused a prominent elevation in the concentrations of MHPG, 5-HIAA and HVA in CSF. However, after a rapid increase, the concentration of MHPG was decreased by 85% from the control values. Haloperidol caused a 3-fold increase in the concentration of HVA, indicating increased DA turnover in the CNS. The method enables the reliable quantitative determination of three major monoamine metabolites in small samples of CSF from freely moving rats and appears to be a useful tool in the evaluation of the validity of the clinically used research methods of monitoring drug-induced alterations in CNS monoaminergic activity by metabolite measurements in CSF.

Monoamine metabolites in human cerebrospinal fluid. HPLC/ED method

Catecholamines and indolealkylamines are of clinical interest in neurological and psychiatric disorders. We measured 3-methoxy-DOPA, 3-methoxy-4-hydroxyphenylglycol, dihydroxyphenylacetic acid, tryptophan, 5-hydroxyindoleacetic acid and homovanillic acid in human cerebrospinal fluid with a simple, sensitive , inexpensive, rapid and accurate procedure using high performance liquid chromatography coupled to an electrochemical detector. Patients with Parkinson's disease have a decrement in homovanillic acid that is reversed by treatment with L-3,4-dihydroxyphenylalanine. After this medication, 3-methoxy-DOPA is measurable in cerebrospinal fluid. Patients with depression show a decrease in serotonin turnover expressed by diminished 5-hydroxyindoleacetic acid content in cerebrospinal fluid. Depressed patients also show low levels of tryptophan. Monoamine metabolites are augmented in patients with subarachnoid hemorrhage.

Plasma and cerebrospinal fluid 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) as indices of brain norepinephrine metabolism in primates

The relationship between MHPG concentration in several brain areas, cisternal CSF and plasma was examined in 26 vervet monkeys. Free MHPG was measured by gas chromatography-mass spectrometry using deuterated MHPG as internal standard. In animals with or without treatment with drugs that alter norepinephrine metabolism, highly significant correlations were found in concentrations of MHPG between the various brain areas, between plasma and CSF, between plasma and brain areas and between CSF and brain areas. The concentration of MHPG in CSF was higher than in plasma and with the exception of occipital cortex, all brain regions contained a higher concentration of MHPG than CSF. This study supports the notion that free MHPG concentrations in plasma and cisternal CSF are useful indices of central noradrenergic activity.