Concentration gradients for monoamine metabolites in lumbar cerebrospinal fluid

Summary 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 (0–4 th ml) and last (21th–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 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.     

Saturable efflux of the peptides RC-160 and Tyr-MIF-1 by different parts of the blood-brain barrier

Peptides have been shown to be transported in the direction of both blood to brain and brain to blood. Although blood to brain transport is known to occur at both the choroid plexus and the capillary bed of the brain, comprising the two major components of the blood-brain barrier, the location of efflux systems for peptides remains largely unstudied. We adapted established methodologies to study this question for two peptides known to be transported out of the brain after injection into the cerebrospinal fluid (CSF): Tyr-MIF-1, transported by peptide transport system (PTS)-1 and RC-160, a somatostatin analog transported by PTS-5. Radioactive iodide, known to be transported out of the brain primarily by the capillaries, also was studied. We found that after injection into brain tissue, RC-160 and iodide were rapidly transported out of the brain by saturable mechanisms. By contrast, efflux of Tyr-MIF-1 was slow and nonsaturable after injection into brain tissue, but rapid and saturable after injection into the lateral ventricle of the brain. Autoradiography confirmed that peptide injected into brain tissue did not diffuse far from the site of injection during the study period. The results indicate that the efflux system for RC-160 is located at least partly at the capillaries and suggest that the major location for the efflux system of Tyr-MIF-1 is at the choroid plexus.     

Evidence for the contribution by the cerebral cortex to 5-hydroxyindoleacetic acid found in the cerebrospinal fluid of cats

Perfusion of artificial CSF from a lateral ventricle to the cerebral cortical subarachnoid space in anaesthetized cats was used to study the contribution of the cerebral cortex to the concentration of 5-hydroxyindoleacetic acid (5-HIAA) in CSF. The technique did not cause rupture of the meninges. The use of [14C]5-HIAA and of probenecid suggested that there was a contribution and also a transport mechanism similar to that in the choroid plexus.     

Intranasal vasotocin decreases cerebrospinal fluid 5-HIAA levels in man

A single dose (10 ng/kg) of the nonapeptide arginine vasotocin (AVT) administered intranasally to healthy young men, significantly decreased 5-HIAA levels in the lumbar cerebrospinal fluid (CSF) 8 hr after its administration. So far, this represents the smallest amount of an active substance able to alter CSF 5-HIAA levels in man. It is suggested that the decrease of CSF 5-HIAA levels after AVT administration reflects an AVT-induced reduction of the brain 5-HT turnover.     

Spinal reflexes and the concentrations of 5-HIAA, MHPG, and HVA in lumbar cereborspinal fluid after spinal lesions in man.

Descending bulbospinal pathways that employ specific neurotransmitter substances are known to be capable of modulating segmental reflex activity in the experimental animal. To determine whether this might also occur in man correlations have been sought between the activity in spinal reflex pathways and the lumbar cerebrospinal fluid (CSF) concentrations of 5-hydroxyindolacetic acid (5-HIAA), 3 methoxy-4-hydroxyphenylglycol (MHPG), and homovanillic acid (HVA) in 12 patients with complete or virtually complete spinal lesions. The concentrations of 5-HIAA and MHPG in lumbar CSF ARE REDUCED AFTER COMPLETE OR VIRTUALLY COMPLETE SPINAL LESIONS IN MAN. This may occur within 18 days of the lesion. MHPG concentrations appear to be inversely related to the level of the lesion. The HVA concentration in lumbar CSF is reduced when there is obstruction of the CSF pathways. No relationship could be demonstrated between the concentrations of 5-HIAA or MHPG in lumbar CSF and the activity in the spinal monosynaptic pathway (estimated from the proportion of the motoneurone pool activated by the Achilles tendon reflex or H reflex) or the activity of a spinal inhibitory mechanism (estimated by the degree of vibratory inhibition of the monosynaptic reflex). Patients with a tonic vibration reflex (TVR) tended to have higher MHPG levels. There appeared to be an association between low CSF HVA and enhanced vibratory inhibition of the monosynaptic reflex in the nine patients whose spinal lesions were complete.     

Role of choroid plexus epithelium in the removal of valproic acid from the central nervous system

Previous experiments suggest the primary route of valproic acid (VPA) removal from the rabbit central nervous system (CNS) is by probenecid-sensitive transporters at the blood-brain barrier but not at the choroid plexus. The purpose of this study was to determine if other transport mechanisms at the choroid plexus played a significant role in the removal of VPA from the CNS. In six rabbits, silicone oil was perfused into both cerebral ventricles and out through the cisterna magna to physically block exchange of VPA between cerebrospinal fluid (CSF) and blood and between brain and CSF. In six control rabbits, perfusion was performed with mock CSF. Both groups received a loading dose followed by continuous intravenous infusion of VPA for 2.10 min. Ventriculocisternal perfusion with silicone oil had no significant effect on the steady-state brain concentrations or brain-to-plasma concentration ratios of VPA, further confirming that efflux of VPA at the choroid plexus is negligible.     

Probenecid sensitive pathway of elimination of dopamine and serotonin metabolites in CSF of the rat

CSF was removed at a constant flow rate of 1 microliter/min from the third ventricle of anesthetized rats. Five microliter CSF samples were directly injected every 15 min into a liquid chromatographic system coupled with an amperometric detector. Mean CSF values for free dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA) were 1.4, 0.9, and 2.6 X 10(-6)M respectively. High doses of probenecid resulted in a linear increase of acidic metabolite concentrations which gave an index of the fractional turnover rates related to the resorption by the weak organic acid carrier. Accumulation rates were 0.24, 0.87, and 1.58 mumol/l/h for DOPAC, HVA and 5-HIAA respectively. This route of elimination was predominant for 5-HIAA while it represented only a small part of total turnover for DOPAC. A high elimination rate constant for HVA validates the use of control levels of this metabolite as an indication of fractional HVA turnover dependent upon probenecid-sensitive carrier.     

CSF monoamine levels in normal-weight bulimia: evidence for abnormal noradrenergic activity.

Normal-weight bulimic patients have disturbed appetite, mood, and neuroendocrine function and often respond to antidepressants. Since these findings suggest abnormalities in brain monoaminergic pathways, the authors measured CSF monoamine concentrations in 27 normal-weight bulimic patients and 14 volunteers. Bulimic patients had a significantly lower mean CSF norepinephrine concentration. Levels of CSF 5-HIAA, the major serotonin metabolite, and CSF HVA, the major dopamine metabolite, were normal, although more frequent binge-eating in bulimic subjects was associated with a significantly lower CSF HVA level. Whether trait- or state-related, monoaminergic disturbances are part of this disorder's neurobiological syndrome. The lower CSF norepinephrine concentration suggests bulimia is not simply a variant of affective disorders.     

Effect of thiamine deficiency on brain serotonin turnover

Serotonin turnover has been investigated in regional brain areas of rats made thiamine deficient by pyrithiamine (PT). Following intracisternal injection of [¹⁴C]5-hydroxytryptamine ([¹⁴C]5-HT), a marked increase in the accumulation of [¹⁴C]5-hydroxyindoleacetic acid ([¹⁴C]5-HIAA) was found in the medulla-pons, hypothalamus and cerebral cortex. [¹⁴C]5-HT levels were normal in all of the brain areas except the cerebral cortex which had an increase of 58%. The ratio of [¹⁴C]5-HIAA/[¹⁴C]5-HT was significantly increased in every brain region of PT-treated rats except the cerebral cortex. Part of this increase in [¹⁴C]5-HIAA was shown to be due to impairment of active transport of this 5-HT metabolite out of the brain. However, increased 5-HT synthesis in the cerebellum, hypothalamus, striatum, hippocampus and cerebral cortex was demonstrated by measurement of 5-HT accumulation after inhibition of brain monoamine oxidase. PT-induced increase in endogenous 5-HIAA in the medulla-pons occurred simultaneously with the onset of neurological signs and both parameters were reversible by thiamine administration. These results suggest that acute thiamine deficiency, induced by PT, both increases brain 5-HT synthesis and impairs 5-HIAA efflux from the brain. There is a close correlation between neurological manifestations and changes in brain 5-HT metabolism in acute thiamine deficiency.     

Central Biogenic Amine Metabolism in Children with the Syndrome of Chronic Multiple Tics of Gilles de la Tourette: Norepinephrine,Serotonin, and Dopamine

Central nervous system metabolism in children with the syndrome of Gilles de la Tourette (TS) and contrasting pediatric patients was assessed by measuring the cerebrospinal fluid (CSF) metabolites of dopamine (homovanillic acid, HVA) and serotonin (5-hydroxyindoleacetic acid, 5-HIAA) with and without the administration of probenecid. Reduced accumulation of CSF HVA and 5-HIAA was found in TS. This may represent a primary decrease in brain turnover of dopamine and serotonin or a long-term adaptation to overactivity in these systems, perhaps as a result of changes in receptor sensitivity. In the CSF of a child with profound TS, an elevated level of the major metabolite of norepine.     

CSF monoamine metabolites in patients and controls: support for a bimodal distribution in major affective disorders

The monoamine metabolites 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in cerebrospinal fluid (CSF) were measured in 38 patients with major affective disorder and 48 age- and sex-matched controls by means of liquid chromatography. Statistical analysis using maximum likelihood normal mixture computations provided evidence for a subgroup of patients characterized by low CSF levels of both 5-HIAA and HVA. In controls, CSF 5-HIAA and HVA levels appeared to be normally distributed when fitted separately, whereas a subgroup of controls characterized by higher values of 5-HIAA and HVA could be discerned when metabolite data were fitted simultaneously. No relationship was found between monoamine levels and suicidal behaviour in patients. A statistically significant relationship was found between CSF 5-HIAA and HVA levels in patients and controls. These data provide supportive evidence for the existence of a subgroup of patients with an abnormal serotonin metabolism as reflected by 5-HIAA, and probably HVA, in CSF.     

Serotoninergic system in dementia of the Alzheimer type. Abnormal forms of 5-hydroxytryptophan and serotonin in cerebrospinal fluid

Serotonin (5-HT), its precursor 5-hydroxytryptophan (5-HTP), and its major metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured in the cerebrospinal fluid (CSF) of 14 patients with dementia of the Alzheimer type (DAT) and in nine controls by high-performance liquid chromatography with a novel multisensor coulometric detection system. Concentrations of both 5-HT and 5-HIAA detected by this system were lower than the concentrations obtained using conventional amperometric detection. This difference was caused by coelution of compounds that could be resolved from 5-HT and 5-HIAA by the multisensor coulometric system. One of the coelution compounds, observed in DAT but not in control CSF, behaved like a partially oxidized 5-HT. A compound behaving like partially oxidized 5-HTP was also observed in DAT CSF. Concentrations of 5-HTP, 5-HT, and 5-HIAA were lower in DAT CSF than in a corresponding fraction of control CSF. These results indicate involvement of the serotoninergic system in DAT and might lead to development of a diagnostic test for DAT.     

CSF concentration gradients of monoamine metabolites in patients with hydrocephalus.

Concentration gradients of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), were assessed in 762 successive CSF fractions (2 ml lumbar CSF) from 15 patients with the adult hydrocephalus syndrome (AHS) and 11 patients with hydrocephalus of other causes (mixed group). A mean volume of 49.6 (SD 11.8) ml CSF was removed in the AHS group and 56.4 (10.2) ml in the mixed group. The CSF was collected with a specially designed carousel fraction collector and the corresponding CSF dynamics were continuously registered by a constant pressure CSF infusion method. Pronounced gradients in CSF HVA and CSF 5-HIAA were seen in both patient groups in the first 25 ml of CSF removed. The concentration curves levelled off, despite the removal of larger amounts of CSF and stabilised at about twice the initial concentrations. This phenomenon has not been described before. Concentrations of HVA and 5-HIAA in the first CSF fraction correlated strongly with concentrations in fractions up to about 40 ml. A positive correlation between the first fraction of CSF HVA and CSF 5-HIAA concentrations and CSF outflow conductance was found in the AHS group. There was no gradient in MHPG. It is suggested that the rostrocaudal gradients in CSF HVA and 5-HIAA may be explained by a downward flow of CSF along the spinal cord with absorption of metabolites occurring during passage. Mixing of CSF from different CSF compartments, extraventricular production sites of CSF, clearance of metabolites to venous blood or extracellular fluid, and CSF outflow conductance are probably important determinants of the plateau phase in patients with hydrocephalus. It is concluded that lumbar CSF does not exclusively reflect the concentrations of HVA, 5-HIAA, or MHPG in the ventricles. It should be noted that these results obtained in patients with hydrocephalus may not be applicable to other groups of patients or normal subjects.     

5-Hydroxyindoleacetic acid in cerebrospinal fluid reflects serotonergic damage induced by 3,4-methylenedioxymethamphetamine in CNS of non-human primates

This study examined whether 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid (CSF) could be used to detect serotonergic damage induced by (+/-)-3,4-methylenedioxymethamphetamine (MDMA) in the central nervous system (CNS) of non-human primates. Monkeys were administered toxic doses of MDMA; two weeks later, the animals were lightly anesthetized with ether and CSF was obtained by means of cervical puncture. Later that same day, the animals were killed for direct determination of CNS serotonin and 5-HIAA concentrations. Monkeys with 73-94% depletions of serotonin and 5-HIAA in brain and 42-45% depletions of serotonin and 5-HIAA in the spinal cord had a 60 +/- 7% reduction of 5-HIAA in CSF, without any change in homovanillic acid (HVA) or 3-methoxy-4-hydroxyphenethyleneglycol (MHPG). These findings indicate that CSF 5-HIAA can be employed to detect central serotonergic damage produced by MDMA in non-human primates, and suggest that CSF 5-HIAA may be useful for detecting MDMA-induced neuronal damage in humans.     

Variation in reproductive outcomes for captive male rhesus macaques (macaca mulatta) differing in CSF 5-hydroxyindoleacetic acid concentrations

In rhesus macaque males, lower than average cerebrospinal fluid (CSF) concentrations of the principle metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA), have been linked to impulsivity, involvement in escalated aggression, failure to elicit consort relationships, production of fewer sperm plugs, and a relatively early age of mortality. Given these potential fitness costs, we performed two studies aimed at elucidating the effects of CSF 5-HIAA on reproduction. Study 1 retrospectively evaluated over a four-year period, the relative reproductive outcome for pairs of adult male rhesus macaques (n = 15) who lived in social groups and who differed in concentrations of CSF 5-HIAA. Study 2 examined the relationship between CSF 5-HIAA and sperm motility and density (n = 12), as a potential mechanism for maintaining variability in CSF 5-HIAA. For Study 1, an average measure from two CSF 5-HIAA samples was calculated for the two males who were present during the time when conception most likely took place (offspring birth date -165 +/- 14 days). Within-pair comparisons of CSF 5-HIAA concentrations between the sire and the non-successful male were drawn for each of the 72 offspring in the study. We found that while sires were typically the male with relatively higher CSF 5-HIAA within the pair, there were no absolute differences in CSF 5-HIAA between males who sired at least one offspring (sires) and those who failed to reproduce (non-sires). Furthermore, while absolute age was not predictive of reproductive outcome, sires with relatively high CSF 5-HIAA also tended to be also relatively older than their competitors. By contrast, for the males with relatively low CSF 5-HIAA who reproduced, sires were relatively younger than the non-sires. These differences in reproductive outcome for males differing in CSF 5-HIAA could not be explained by variability in sperm quantity or quality as we did not find evidence of a relationship between CSF 5-HIAA and either sperm measure. The results of this study suggest that as serotonergic function affects many aspects of behavior and survivorship, it might also be associated with reproductive outcome and different life-history strategies for males differing in concentrations of CSF 5-HIAA.     

Serotoninergic development in the postnatal rat brain

Summary Various characteristics of the developing serotoninergic system in the brain of rats aged 1 to 28 days were studied biochemically.The levels of the precursor amino acid tryptophan showed a maximal increase in the blood, brain and cerebrospinal fluid (CSF) during the 7th and 10th postnatal days. The development of tryptophan hydroxylase activity measuredin vivo by means of 5-hydroxytryptophan (5-HTP) accumulation after NSD 1015 was closely related to the 5-hydroxytryptamine (5-HT) levels at the various ages. 5-HTP accumulation and 5-HT levels increased most markedly after the second postnatal week. 5-Hydroxyindoleacetic acid (5-HIAA) levels were found to increase rapidly in the brain but somewhat more slowly in the CSF during the second week of postnatal development. Regional studies of 5-HTP accumulation after NSD 1015, 5-HT and 5-HIAA levels indicated a caudal to rostral way of maturation.The disappearance of 5-HT was measured after inhibition of tryptophan hydroxylase with H 22/54. The half-life generally decreased in the various brain parts with advancing age, and in the younger animals the shortest half-life was found in the most caudal brain parts. At 28 days of age the half-life was similar in all brain parts studied. These results indicate the existence of an adult like nerve impulse flow in the 5-HT neurons in the brain stem region of the newborn rats. The results from this investigation clearly indicate that the maturation of the different biochemical parameters of the 5-HT pathways develop in a caudal to rostral direction.The study also supports the view that tryptophan hydroxylase may be the limiting step in the development of the serotoninergic system.     

Changes in CSF neurotransmitters in infantile spasms

Cerebrospinal fluid (CSF) from 7 patients with infantile spasms (mean age: 6.7 months) was collected before and after treatment with adrenocorticotropic hormone (ACTH). The concentration of neurotransmitter metabolites was analyzed using high-performance liquid chromatography and compared to the metabolite concentration in the CSF from 7 age-matched controls (mean age: 6.1 months). Pretreatment levels of CSF 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid, 3-methoxy-4-hydroxyphenyl glycol (MHPG), and kynurenine were significantly lower in infantile spasm patients compared to controls. Following treatment, marked increases in 5-HIAA and decreases in kynurenine levels were observed in the CSF of the 5 infants whose seizures were eliminated or reduced by ACTH. In the 2 nonresponders 5-HIAA levels decreased. The level of MHPG was reduced slightly in 5 infants, including the 2 nonresponders, and was increased in 2 responders. CSF homovanillic acid levels increased in 4 infantile spasm infants and decreased in 3 following ACTH. These data demonstrate that the presence of seizures in infantile spasms is associated with a significant decrease in serotonergic activity and that elimination of seizures by ACTH is accompanied by increased serotonin turnover. The simultaneous increase of 5-HIAA and decrease of kynurenine, an alternate metabolite of tryptophan, suggests an underlying disturbance of tryptophan metabolism in infantile spasms. The possibility that elimination of seizures by ACTH may be related to decreased production of certain kynurenine metabolites, particularly quinolinic acid, is discussed.     

3-Methoxy-4-hydroxy-phenylglycol sulfate (MOPEG-SO4) in ventricular and cisternal cerebrospinal fluid of dogs.

Cerebrospinal fluid was collected from the lateral ventricles and cisternal space from beagle dogs under light pentobarbital anesthesia. Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglyco-sulfate (MOPEG-SO4) levels in the liquor taken from these two regions were evaluated, and the ventricular-cisternal ratio (V/C) was calculated for each monoamine metabolite. A marked similarity in the V/C ratio of 6:1 for 5-HIAA and 5:1 for MOPEG-SO4, as compared to a much higher V/C ratio of 18:1 for HVA, perhaps reflects the more diffuse distribution of norepinephrine and serotonin, precursor amines, as compared to dopamine in the CNS and also emphasizes the probable existence of an active transport mechanism for the removal of MOPEG-SO4, as has been well documented for 5-HIAA and HVA.     

The relationship of cerebrospinal fluid monoamine metabolites with clinical response to tetrahydroaminoacridine in patients with Alzheimer's disease

Summary The effect of tetrahydroaminoacridine (THA) on the cerebrospinal fluid (CSF) monoamine metabolites was studied in 22 patients with Alzheimer's disease in an open treatment trial. The CSF monoamine metabolites were assayed at baseline and after 4 weeks' active THA treatment with 100 mg/d. A statistically significant increase in the CSF homovanillic acid (HVA) and in 5-hydroxyindoleacetic acid (5-HIAA) content was found. The increase of the CSF 5-HIAA level correlated significantly with improvement in cognitive tests and in the Instrumental Activities of Daily Living Scale. We conclude that besides its anticholinesterase activity THA enhances also the monoaminergic neurotransmission in the brain and that the clinical improvement during THA treatment may be partly mediated through the monoaminergic system.     

Physiology and pathology of the blood-brain barrier: implications for microbial pathogenesis, drug delivery and neurodegenerative disorders

The blood-brain barrier (BBB) regulates the passage of solutes between the CNS and the blood. The BBB not only restricts the entry of serum proteins into the CNS, but it also controls the passage of nutrients, electrolytes, vitamins, minerals, free fatty acids, peptides, and regulatory proteins in both the brain to blood and blood to brain direction. The BBB performs these functions through a number of saturable and non-saturable mechanisms. For example, efflux (CNS to blood) mechanisms regulate the levels of nutrients and minerals in the CSF, detoxify the CNS, reinforce the impermeability of the BBB against circulating toxins and many drugs, secrete CNS-originating substances into the blood, and drain substances directly into the cervical lymphatic nodes. Influx mechanisms control the homeostatic environment of the CNS, supply the brain with nutrients, and help to integrate CNS and peripheral functions. These mechanisms are altered in and can be the basis for disease and many of these systems are altered in neuroAIDS. We review here examples of several diseases in which the functions of the BBB are altered, and some conditions, such as alcoholism, multiple sclerosis, obesity, and a subtype of mental retardation, where those altered functions may underlie the pathophysiology. Finally, we consider some of the ways in which these aspects of the BBB could be active in neuroAIDS, including the efflux of anti-virals, the transport of virus by adsorptive endocytosis, egress routes for HIV-1 via brain lymphatics, and the release of neurotoxins from brain endothelial cells.