Effect of age on cisternal cerebrospinal fluid concentrations of monoamine metabolites in nonhuman primates

There are conflicting reports of the effects of aging on human neurotransmitter systems as estimated by monoamine metabolite concentrations in cerebrospinal fluid (CSF). These discrepancies may be due to sampling site, age or sex of the subjects or other variables that affect CSF metabolite determinations. Cisternal CSF concentrations of homovanillic acid (HVA), 3-methoxy-4-hydroxyphenyl-ethylene glycol (MHPG) and 5-hydroxyindoleacetic acid (5-HIAA), major metabolites of dopamine, norepinephrine and serotonin, respectively, were measured in rhesus monkeys (Macaca mulatta) of two age groups. Concentrations of HVA and MHPG were significantly lower in the older group of monkeys, whereas no changes in 5-HIAA were found. This supports the hypothesis that brain catecholamine concentrations decline with age.     

Higher Orexin A levels in lumbar compared to ventricular CSF: A study in idiopathic normal pressure hydrocephalus

Orexin A (ORX-A) is implicated in the regulation of various physiological processes, including sleep/wake cycles and reward/motivation. The hypothalamic ORX-A neurons project throughout the brain and spinal cord. In the present study we established and compared ORX-A levels in lumbar and ventricular cerebrospinal fluid (CSF) samples, drawn from idiopathic normal pressure hydrocephalus (INPH) patients, during respectively, lumbar puncture and shunt placement. Ventricular and lumbar CSF levels of total protein and of the dopamine, serotonin and norepinephrine metabolites HVA, 5-HIAA and MHPG respectively, were also estimated. ORX-A was quantified using a commercially available radioimmunoassay kit. Neurotransmitter metabolites were quantified by high performance liquid chromatography. Expectedly, HVA and 5-HIAA levels were significantly higher and total protein levels lower in ventricular compared to lumbar CSF while there were no differences in MHPG levels. However, in contrast to HVA and 5-HIAA and similar to total protein, lumbar ORX-A levels were significantly higher than ventricular levels. The higher lumbar compared to ventricular ORX-A levels may reflect elevated contributions from the spinal cord. The finding of a ventriculo-lumbar difference for ORX-A should be considered in studies utilizing its CSF levels in assessing Orexin system status.     

HOMOVANILLIC ACID AND 3-METHOXY-4- HYDROXYPHENYLETHYLENEGLYCOL PRODUCTION BY THE MONKEY SPINAL CORD

The release of homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) into CSF by the monkey spinal cord was investigated with spinal subarachnoid perfusion of 20 rhesus monkeys. The preperfusion concentration of HVA in lumbar CSF was 365 ng/ml and in cisternal CSF was 365 ng/ml, while the concentrations of MHPG were 28.3 and 40.4 ng/ml respectively. HVA originating from the spinal cord appeared in the perfusate at a rate of 2.4 and MHPG at 1.4 ng/min. Treatment with probenecid either intraperitoneally or intrathecally did not alter the rate of release into CSF of these metabolites by the spinal cord but did significantly increase the rate of appearance in the cisterna magna of HVA originating from the brain. MHPG and HVA in lumbar CSF are therefore derived in part from spinal cord metabolism.     

Biochemical evidence for simultaneous activation of multiple locus coeruleus efferents

To test the hypothesis that all locus coeruleus projections are simultaneously activated when the locus coeruleus cells fire, the norepinephrine metabolite 3-methoxy-4-hydroxyphenethyleneglycol was assayed in four regions of the central nervous system innervated by the locus coeruleus after three treatments designed to increase locus coeruleus firing in rats. Electrical stimulation of the locus coeruleus, intraperitoneal piperoxan treatment, and electric footschock all significantly increased MHPG levels in rat cerebral cortex, cerebellum, hippocampus, and spinal cord. The magnitude of MHPG increase was greater after locus coeruleus stimulation than after footshock or piperoxan. No significant differences between increases in the above brain regions were found within each treatment group.     

Ventricular Cerebrospinal Fluid Monoamine Transmitter and Metabolite Concentrations Reflect Human Brain Neurochemistry in Autopsy Cases

Concentrations of dopamine (DA), its metabolites 3-methoxytyramine and homovanillic acid (HVA), noradrenaline (NA), its metabolites normetanephrine (NM) and 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxytryptamine (5-HT, serotonin), and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured in 14 brain regions and in CSF from the third ventricle of 27 human autopsy cases. In addition, in six cases, lumbar CSF was obtained. Monoamine concentrations were determined by reversed-phase liquid chromatography with electrochemical detection. Ventricular/lumbar CSF ratios indicated persistence of rostrocaudal gradients for HVA and 5-HIAA post mortem. Ventricular CSF concentrations of DA and HVA correlated positively with striatal DA and HVA. CSF NA correlated positively with NA in hypothalamus, and CSF MHPG with levels of MHPG in hypothalamus, temporal cortex, and pons, whereas CSF NM concentration showed positive correlations with NM in striatum, pons, cingulate cortex, and olfactory tubercle. CSF 5-HT concentrations correlated positively with 5-HT in caudate nucleus, whereas the concentration of CSF 5-HIAA correlated to 5-HIAA levels in thalamus, hypothalamus, and the cortical areas. These data suggest a specific topographic origin for monoamine neurotransmitters and their metabolites in human ventricular CSF and support the contention that CSF measurements are useful indices of central monoaminergic activity in man.     

Concentrations of catecholamines and indoleamines in the central nervous system of Wriggle mouse Sagami

1. The concentrations of norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the central nervous system of Wriggle mouse Sagami (WMS), which is a new ataxic mutant mouse, were studied. 2. NE and MHPG levels were increased most remarkably in the cerebellum. 3. 5-HT and 5-HIAA levels were increased most remarkably in the brain stem and spinal cord. 4. The present results suggest enhancement of catecholamine and indoleamine metabolism in the cerebellum and bulbospinal cord, respectively, of the WMS, and these changes seem relevant to the specific motor dysfunction of the WMS.     

Delayed dispersal and elevated monoaminergic activity in free-ranging rhesus monkeys

Male rhesus monkeys typically disperse from their groups of birth when they are between 3 and 5 years of age. Some males, however, delay dispersal from their natal groups until after they are 5 years old. The current study evaluated central monoaminergic neurotransmitter activity as a potential correlate of such “delayed” dispersal among 54 randomly selected adolescent and adult male rhesus monkeys (Macaca mulatta) captured on Cayo Santiago during an annual trapping season. Specifically, cerebrospinal fluid (CSF) concentrations of 5-hydroxyindoleacetic acid (5-HIAA, a serotonin metabolite), 3-methoxy-4-hydroxyphenylglycol (MHPG, a norepinephrine metabolite), and homovanillic acid (HVA, a dopamine metabolite) were compared in monkeys 60 months of age or more that had either dispersed (n = 33) or were still in their natal groups (n = 5). The monkeys still in their natal groups had higher CSF concentrations of both 5-HIAA and HVA (but not MHPG) than did the animals that had emigrated (Ps < 0.05). Subsequent analysis indicated that only 5-HIAA independently differentiated dispersing monkeys from delayed dispensers. Of monkeys less than 60 months of age (n = 16), only two had dispersed from their natal groups; in this age class, there were no significant differences between dispersing and natal individuals in any CSF monoaminergic metabolite (all Ps = NS). Finally, there was no difference in the CSF 5-HIAA concentrations of the five delayed dispersers and those of younger animals (P = NS), suggesting a failure to experience the frequently reported adolescent decline in serotonergic activity. In contrast, the CSF 5-HIAA concentrations of the dispersing animals were lower than those of the younger animals (P < 0.05), consistent with either an agerelated decline or an effect of dispersal per se. © 1995 Wiley-Liss, Inc.     

The contribution of CNS MHPG to plasma MHPG in the rat

Two different experimental approaches were used to determine the central nervous system (CNS) contribution to plasma total 3-methoxy-4-hydroxyphenylglycol (MHPG) levels in the rat. One experiment, using intracisternal injection of 6-hydroxydopamine (6-OHDA), depleted total forebrain norepinephrine (NE) and MHPG to 26 and 34% of control values, respectively. In spite of the substantial reduction in CNS MHPG, plasma MHPG was not significantly different from control values. The second experiment used clonidine and debrisoquine to differentially impair central and peripheral NE metabolism. The results of this experiment confirm those of the 6-OHDA experiment in suggesting that the CNS contribution to plasma MHPG in the rat is negligeable.     

Quinolinic acid is extruded from the brain by a probenecid-sensitive carrier system: a quantitative analysis

Although the neurotoxic tryptophan-kynurenine pathway metabolite quinolinic acid originates in brain by both local de novo synthesis and entry from blood, its concentrations in brain parenchyma, extracellular fluid, and CSF are normally below blood values. In the present study, an intraperitoneal injection of probenecid (400 mg/kg), an established inhibitor of acid metabolite transport in brain, into gerbils, increased quinolinic acid concentrations in striatal homogenates, CSF, serum, and homogenates of kidney and liver. Direct administration of probenecid (10 mM) into the brain compartment via an in vivo microdialysis probe implanted into the striatum also caused a progressive elevation in both quinolinic acid and homovanillic acid concentrations in the extracellular fluid compartment but was without effect on serum quinolinic acid levels. A model of microdialysis transport showed that the elevations in extracellular fluid quinolinic acid and homovanillic acid levels following intrastriatal application are consistent with probenecid block of a microvascular acid transport mechanism. We conclude that quinolinic acid in brain is maintained at concentrations below blood levels largely by active extrusion via a probenecid-sensitive carrier system.     

Effects of yohimbine and idazoxan on monoamine metabolites in rat cerebrospinal fluid

Effects of two alpha 2-adrenoceptor antagonists, idazoxan and yohimbine, on the concentrations of monoamine metabolites in cisternal cerebrospinal fluid (CSF) of freely moving rats were investigated. Both drugs caused a dose-dependent, up to 250% increase in the concentration of 3-methoxy-4-hydroxyphenylglycol (MHPG) in CSF indicating enhanced release, metabolism and turnover of noradrenaline in the central nervous system (CNS). In addition, a similar increase in homovanillic acid (HVA) in CSF was observed, while the level of 5-hydroxyindoleacetic acid was unchanged. The present results demonstrate the usefulness of monitoring drug-induced alterations in noradrenergic activity in the CNS by measurement of free MHPG in repeatedly collected cisternal CSF samples from awake rats. The possibility that the observed increase in the concentration of HVA after the highly specific alpha 2-antagonist idazoxan reflects increased noradrenergic rather than dopaminergic neuronal activity is discussed.     

The effect of probenecid on catecholamine metabolites in human cerebrospinal fluid analyzed by mass fragmentography.

A gas chromatography-mass fragmentography (GC-MS) method was used to measure homovanillic acid (HVA), vanillylmandelic acid (VMA) and 3-methoxy-4-hydroxyphenethylene glycol (MHPG) in lumbar cerebrospinal fluid (CSF) of 31 patients before and after treatment with probenecid. HVA values increased from 24.6 ± 2.6 S.E.M. to 210 ± 17 ng/ml. The increase in VMA was from 1.06 ± 0.23 to 2.22 ± 0.17 ng/ml and that of MHPG was from 12.2 ± 1.08 to 15.6 ± 1.27 ng/ml. All increases were significant (p = < .01). The results for MHPG and HVA are consistent with results of earlier studies using different methods. VMA concentrations increased significantly but at a rate much lower than those of HVA.     

In-use stability of monoamine metabolites in human cerebrospinal fluid

Cerebrospinal fluid (CSF) concentrations of the monoamine metabolites homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA) are commonly used to provide information about central nervous system (CNS) dopaminergic and serotonergic activity. However, little attention has been given to the effects of sample handling on the concentrations of these compounds in human CSF. Using high-performance liquid chromatography (HPLC) with electrochemical detection, we observed that, in CSF stored at −80°C, concentrations of the serotonin metabolite 5-HIAA and the dopamine metabolite HVA remained unchanged through six 1-h and six 24-h freeze–thaw cycles. Exposure to bright room light (3 h, 1230 lux) resulted in a 5-HIAA concentration that was 96.3±2.0% of the initial and an HVA concentration that was 98.8±1.03% of initial. The pH of the CSF significantly increased during both freeze–thaw series and while maintained on ice (4°C). These results demonstrate the in-use stability of 5-HIAA and HVA in human CSF under commonly-encountered laboratory conditions.     

Cerebrospinal fluid gradients of acetylcholinesterase and butyrylcholinesterase activity in healthy aging

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities were measured in 13 sequential 2 ml aliquots of cerebrospinal fluid (CSF) obtained by lumbar puncture from 7 young and 7 elderly healthy normal subjects. The slopes of the rostrocaudal gradients of AChE and BChE were calculated and compared to those of total protein concentration and the major dopaminergic metabolite homovanillic acid (HVA), for which a pronounced rostrocaudal gradient (with highest concentrations of HVA in more rostral CSF) is consistent with HVA originating primarily from the brain. AChE activity was higher in more caudal fractions of young, but not elderly subjects and there was a significant difference between the mean AChE gradient slopes in the young and old groups. These results suggest that the spinal cord makes an important contribution to AChE activity in lumbar CSF. Furthermore, the absence of a negative AChE gradient in elderly subjects may be the result of a greater rate of entry of cerebral AChE into CSF, possibly as a consequence of an increased ventricular surface area and shorter diffusion distances in atrophic elderly brains. In contrast to AChE, BChE activity and total protein concentrations were higher in more caudal CSF fractions of not only young but also old subjects. In addition, there was a significant correlation between the gradient slopes of BChE activity and total protein concentrations, suggesting that the majority of BChE activity in lumbar CSF derives from the same source as the majority of total protein, namely plasma. The diffuse (i.e. brain and spinal cord) origin of AChE in lumbar CSF would explain the relatively modest changes in lumbar CSF AChE activity in diseases involving certain central cholinergic systems, most notably Alzheimer's disease.     

Monoamine Neurotransmitter Metabolites in the Cerebrospinal Fluid of a Group of Hybrid Baboons (Papio hamadryas × P. anubis)

Comparatively little is known about the pathways of proximate causation that link divergent genotypes, via neurophysiological differences, to distinct, species-specific social behaviors and systems. One approach to the problem compares gross activity levels of monoamine neurotransmitters (norepinephrine, dopamine, and serotonin), evidenced by their metabolites —3-methoxy-4-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA), respectively— in cerebrospinal fluid (CSF). We have applied this method to Papio hamadryas and P. anubis, closely related baboon species with divergent social behavior, living in the Awash National Park (ANP), Ethiopia. We had previously shown that adult males of the two species differ in the ratio of HVA to 5-HIAA, and in concentrations of MHPG and HVA, but not 5-HIAA. Here, we compare monoamine metabolite levels of the parental species with those of 49 members of a naturally formed, multigenerational hamadryas × anubis hybrid group. We cage-trapped the baboons in July 1998, sampled their CSF by cisternal puncture, and assayed monoamine metabolites by high-performance liquid chromatography. Previous findings suggested, anomalously, that hybrid males showed the high 5-HIAA levels predicted by the low-serotonin–early-dispersal hypothesis (originally based on observation of rhesus macaques, Macaca mulatta), while hamadryas did not. The present study failed to find higher 5-HIAA levels in hybrids, resolving the anomaly, but leaving the previous result unexplained. Among adult females (underrepresented in our sample) and juveniles, metabolite levels of the hybrids did not differ significantly from either parental species. Overall, adult male hybrids resembled anubis in HVA and HVA/5-HIAA ratio, but did not show the low MHPG levels characteristic of that species. Consistent with a significant genetic influence on species differences in these metabolites, the adult hybrids showed intermediate means and greater intra-population diversity than the parental species for most variables, but showed no indication of hybrid dysgenesis in the form of low intermetabolite correlation. To the contrary, an enhanced HVA–MHPG correlation in the hybrids suggested a species-associated factor (not necessarily genetic) influencing both of these monoamine neurotransmitter systems.     

Central and peripheral noradrenergic tone in primary hypertension

The contents of norepinephrine (NE), epinephrine (E), dopamine (DA), normetanephrine (NMN), and 4-hydroxy-3-methoxyphenylethylene glycol (MHPG) were measured in the plasma and cerebrospinal fluid (CSF) of 66 patients with primary hypertension and 24 patients with normal blood pressure and minor neurological disorders. Plasma and CSF NE and NMN concentrations were raised in the hypertensive patients. The plasma and CSF NE levels and arterial blood pressure of a small subset of hypertensive patients were normalized after clonidine therapy. In hypertensive patients the content of DA was lower and the ratio of NE/DA was greater; CSF and plasma NE contents were related to the level of arterial blood pressure; and the content of MHPG in CSF was linked strongly with NE content in plasma and CSF and to the level of arterial blood pressure. Thus both central sympathetic nerve tone and peripheral sympathetic nerve tone were enhanced in young patients with uncomplicated hypertension. The elevated levels of neurohormones and their metabolites in some patients with primary hypertension may be related to increased synthesis and release of neural NE and may be pathogenic in the blood pressure elevation.     

ON THE ELIMINATION OF CENTRALLY FORMED 5-HYDROXYINDOLEACETIC ACID BY CEREBROSPINAL FLUID AND URINE

Abstract— In rats, the release of centrally formed 5-hydroxyindoleacetic acid (5-HIAA) into brain and spinal cord perfusates and urine was measured. Data from spinal cord perfusion of anaesthetized rats indicate that more than about 36% of the spinal production (122ng/h) of 5-HIAA is eliminated via the cerebrospinal fluid (CSF). More than 30% of cerebrally formed 5-HIAA (265.0 ng/h) was calculated to be released into ventricular-cisternal perfusates. Of the total amount of 5-HIAA found in the urine we estimated that about 8% originates in the central nervous system (CNS).
In probenecid treated animals there was a substantial increase in the outflow of 5-HIAA in both perfusion systems. In the combined perfusion experiments no proportional increase of the cerebral contribution to the cisternal outflow was found after probenecid. Our data indicate that a significant proportion of centrally formed 5-HIAA is eliminated by the CSF. No evidence was found for an increased contribution of cerebral 5-HIAA to lumbar CSF after application of the probenecid test. Urinary levels of 5-HIAA do not reflect quantitatively central 5-hydroxytryptamine metabolism.     

Reduced concentrations of arginine vasopressin and MHPG in lumbar CSF of patients with Korsakoff's psychosis

The concentrations of arginine vasopressin (AVP), somatostatin (SS), and the primary brain metabolites of norepinephrine (MHPG), serotonin (5-HIAA), and dopamine (HVA) were measured in samples of lumbar CSF obtained from ten amnesics with Korsakoff's psychosis, four patients with a history of Korsakoff's psychosis who had recovered from the amnesic symptoms of this disease, and control subjects. Significant deficits were observed in the amnesic group for AVP and MHPG, but not for the other substances measured. Subjects who had recovered from the amnesic symptoms of Korsakoff's psychosis had increased concentrations of AVP and MHPG, but not of SS or the other monoamine metabolites.     

Impaired noradrenergic transmission in schizophrenia?

Recently, increased brain and spinal fluid (CSF) norepinephrine (NE), and a decreased cAMP response to prostaglandin E₁ (PgE₁) stimulation of platelet NE sensitive adenylcyclase were observed in some schizophrenic patients. Low $\text{CSF}$ dopamine-beta-hydroxylase (DBH) activity was related to brain atrophy, whereas high $\text{plasma}$ DBH was associated with tardive dyskinesia. Increased NE (in brain and CSF) and 3-methoxy-4-hydroxy-phenylglycol (MHPG) levels and decreased plasma DBH activity in the brain were associated with a diagnosis of paranoid schizophrenia. Impaired NE transmission in schizophrenia may relate to disturbances in the autonomic nervous system, deficits in attention and information processing and to an impaired ability to deal with stress. Although pharmacological studies have suggested a major role for dopamine (DA) in schizophrenic psychosis, this review indicates the need for further exploration of the NE system. Future studies should address the relationship with DA, the autonomic nervous system (ANS), cerebral blood flow, brain metabolism, stress response, negative and prodromal symptoms.     

Tetrahydrobiopterin administration to rhesus macaques

Tetrahydrobiopterin, the hydroxylase cofactor (BH₄) was administered (i.v. 20 mg/kg) to Rhesus monkeys. Within 90 min of its administration CSF cofactor levels increased significantly above baseline levels. Peak CSF levels were attained at 90–180 min time period following cofactor injection and returned to baseline gradually over the next 15 hrs. The increased brain cofactor levels had no apparent effect on synthesis of dopamine, norepinephrine or serotonin as evidenced by a lack of change in the levels of the metabolites homovalillic acid, 3-methoxy-4-hydroxyphenyleneglycol, and 5-hydroxyindoleacetic acid. The present resultsAbbreviations BH₄ tetrahydrobiopterin - CSF cerebrospinal fluid - 5-HIAA 5-hydroxyindoleacetic acid - HAV homovanillic acid - MHPG 3-methoxy-4-hydroxyphenyleneglycol Supported by Dystonia Medical Research Foundation, 9615 Brighton Way, Suite 416, Beverly Hills, California 90210     

Serial cerebrospinal fluid tryptophan and 5-hydroxy indoleacetic acid concentrations in healthy human subjects

The role of the serotonergic system in the pathogenesis of behavioral disorders such as depression, alcoholism, obsessive-compulsive disorder, and violence is not completely understood. Measurement of the concentration of neurotransmitters and their metabolites in cerebrospinal fluid (CSF) is considered among the most valid, albeit indirect, methods of assessing central nervous system function in man. However, most studies in humans have measured lumbar CSF concentrations only at single time points, thus not taking into account rhythmic or episodic variations in levels of neurotransmitters, precursors, or metabolites. We have continuously sampled lumbar CSF via subarachnoid catheter in 12 healthy volunteers, aged 20-65 years. One ml (every 10 min) CSF samples were collected at a rate of 0.1ml/min for 24-hour (h), and the levels of tryptophan (TRP) and 5-hydroxy indoleacetic acid (5-HIAA) were measured. Variability across all 12 subjects was significantly greater (P < 0.0001) than the variability seen in repeated analysis of a reference CSF sample for both 5-HIAA (32.0% vs 7.9%) and TRP (25.4% vs 7.0%), confirming the presence of significant biological variability during the 24-hr period examined. This variability could not be explained solely by meal related effects. Cosinor analysis of the 24-hr TRP concentrations from all subjects revealed a significant diurnal pattern in CSF TRP levels, whereas the 5-HIAA data were less consistent. These studies indicate that long-term serial CSF sampling reveals diurnal and biological variability not evident in studies based on single CSF samples.