Increasing Central Serotonin with 5-hydroxytryptophan Disrupts the Inhibition of Social Gaze in Nonhuman Primates.

To competently navigate the world, individuals must flexibly balance distinct aspects of social gaze, orienting toward others and inhibiting orienting responses, depending on the context. These behaviors are often disrupted amongst patient populations treated with serotonergic drugs. However, those in the field lack a clear understanding of how the serotonergic system mediates social orienting and inhibiting behaviors. Here, we tested how increasing central concentrations of serotonin with the direct precursor 5-hydroxytryptophan (5-HTP) would modulate the ability of rhesus macaques (both sexes) to use eye movements to flexibly orient to, or inhibit orienting to, faces. Systemic administrations of 5-HTP effectively increased central serotonin levels and impaired flexible orientation and inhibition. Critically, 5-HTP selectively impaired the ability of monkeys to inhibit orienting to face images, whereas it similarly impaired orienting to face and control images. 5-HTP also caused monkeys to perseverate on their gaze responses, making them worse at flexibly switching between orienting and inhibiting behaviors. Furthermore, the effects of 5-HTP on performance correlated with a constriction of the pupil, an increased time to initiate trials, and an increased reaction time, suggesting that the disruptive effects of 5-HTP on social gaze behaviors are likely driven by a downregulation of arousal and motivational states. Together, these findings provide causal evidence for a modulatory relationship between 5-HTP and social gaze behaviors in nonhuman primates and offer translational insights for the role of the serotonergic system in social gaze.SIGNIFICANCE STATEMENT Behavioral changes arising from pharmacological agents that target serotonergic functions are complex and difficult to predict. Here, we examined the causal impacts of administering the direct precursor of serotonin, 5-HTP, on orienting and inhibiting social gaze in nonhuman primates. 5-HTP increased central concentrations of serotonin and selectively impaired the ability of monkeys to inhibit orienting to faces while similarly impairing the ability of monkeys to orient to face and control images. These behavioral gaze impairments were systematically associated with a downregulation of arousal and motivational states, indexed by pupil constriction, increased time to initiate trials, and increased reaction time. These findings provide a causal link between 5-HTP and social gaze behaviors in nonhuman primates and provide translational insights about serotonergic interventions.

The effects of 5-hydroxytryptophan on attention and central serotonin neurochemistry in the rhesus macaque.

Psychiatric disorders, particularly depression and anxiety, are often associated with impaired serotonergic function. However, serotonergic interventions yield inconsistent effects on behavioral impairments. To better understand serotonin's role in these pathologies, we investigated the role of serotonin in a behavior frequently impaired in depression and anxiety, attention. In this study, we used a quantitative, repeated, within-subject, design to test how L-5-hydroxytryptophan (5-HTP), the immediate serotonin precursor, modulates central serotoninergic function and attention in macaques. We observed that intramuscular 5-HTP administration increased cisternal cerebrospinal fluid (CSF) 5-HTP and serotonin. In addition, individuals' baseline looking duration, during saline sessions, predicted the direction and magnitude in which 5-HTP modulated attention. We found that 5-HTP decreased looking duration in animals with high baseline attention, but increased looking duration in low baseline attention animals. Furthermore, individual differences in 5-HTP's effects were also reflected in how engaged individuals were in the task and how they allocated attention to salient facial features-the eyes and mouth-of stimulus animals. However, 5-HTP constricted pupil size in all animals, suggesting that the bi-directional effects of 5-HTP cannot be explained by serotonin-mediated changes in autonomic arousal. Critically, high and low baseline attention animals exhibited different baseline CSF concentrations of 5-HTP and serotonin, an index of extracellular functionally active serotonin. Thus, our results suggest that baseline central serotonergic functioning may underlie and predict variation in serotonin's effects on cognitive operation. Our findings may help inform serotonin's role in psychopathology and help clinicians predict how serotonergic interventions will influence pathologies.

Metabolomics Identifies Multiple Candidate Biomarkers to Diagnose and Stage Human African Trypanosomiasis.

Treatment for human African trypanosomiasis is dependent on the species of trypanosome causing the disease and the stage of the disease (stage 1 defined by parasites being present in blood and lymphatics whilst for stage 2, parasites are found beyond the blood-brain barrier in the cerebrospinal fluid (CSF)). Currently, staging relies upon detecting the very low number of parasites or elevated white blood cell numbers in CSF. Improved staging is desirable, as is the elimination of the need for lumbar puncture. Here we use metabolomics to probe samples of CSF, plasma and urine from 40 Angolan patients infected with Trypanosoma brucei gambiense, at different disease stages. Urine samples provided no robust markers indicative of infection or stage of infection due to inherent variability in urine concentrations. Biomarkers in CSF were able to distinguish patients at stage 1 or advanced stage 2 with absolute specificity. Eleven metabolites clearly distinguished the stage in most patients and two of these (neopterin and 5-hydroxytryptophan) showed 100% specificity and sensitivity between our stage 1 and advanced stage 2 samples. Neopterin is an inflammatory biomarker previously shown in CSF of stage 2 but not stage 1 patients. 5-hydroxytryptophan is an important metabolite in the serotonin synthetic pathway, the key pathway in determining somnolence, thus offering a possible link to the eponymous symptoms of "sleeping sickness". Plasma also yielded several biomarkers clearly indicative of the presence (87% sensitivity and 95% specificity) and stage of disease (92% sensitivity and 81% specificity). A logistic regression model including these metabolites showed clear separation of patients being either at stage 1 or advanced stage 2 or indeed diseased (both stages) versus control.

Secondary abnormalities of neurotransmitters in infants with neurological disorders.

Neurotransmitters are essential in young children for differentiation and neuronal growth of the developing nervous system. We aimed to identify possible factors related to secondary neurotransmitter abnormalities in pediatric patients with neurological disorders. We analyzed cerebrospinal fluid (CSF) and biogenic amine metabolites in 56 infants (33 males, 23 females; mean age 5.8mo [SD 4.1mo] range 1d-1y) with neurological disorders whose aetiology was initially unknown. Patients were classified into three clinical phenotypes: epileptic encephalopathy, severe motor impairment, and non-specific manifestations. All patients showed normal results for screening of inborn errors of metabolism. We report clinical, neuroimaging, and follow-up data. Among the patients studied, 10 had low homovanillic acid (HVA) levels and in four patients, 5-hydroxyindoleacetic acid (5-HIAA) was also reduced. Patients with neonatal onset had significantly lower levels of HVA than a comparison group. HVA deficiency was also associated with severe motor impairment and the final diagnosis related to neurodegenerative disorders. 5-HIAA values tended to be decreased in patients with brain cortical atrophy. The possibility of treating patients with L-Dopa and 5-hydroxytryptophan, in order to improve their neurological function and maturation, may be considered.

A study of tryptophan metabolism via serotonin in ventricular cerebrospinal fluid in HIV-1 infection using a neuroendoscopic technique.

In this paper we report the study of tryptophan metabolism via serotonin in ventricular CSF in HIV-1 infection in order to investigate the origin of tryptophan metabolites in the human brain. The patients (n=4) were affected with non-communicating hydrocephalus. One of these also was suffering from HIV-1 infection. The CSF was withdrawn from different sites of the cerebral cavity with a neuroendoscopic procedure which allows an accurate exploration of all the cerebral ventricles. The measurement of tryptophan, 5-hydroxytryptophan, serotonin, 5-hydroxyindoleacetic acid, and melatonin was carried out by HPLC with fluorometric detection. In HIV-1 infection the highest concentration of tryptophan is present in the CSF of the choroid plexus; however, the levels are markedly lower than those in hydrocephalic individuals (control group). 5-Hydroxytryptophan CSF content is higher in HIV-1 infection than in hydrocephalic controls in all districts examined. Regarding serotonin, a great difference appears in the choroid plexus and in the pituitary recess between the HIV-1 infected patient and the control group. The values of 5-hydroxyindoleacetic acid are much lower in the CSF of the HIV-1 infected patient than in hydrocephalic controls. Melatonin levels appear to fluctuate largely but, in the HIV-1 infection, a great variability is present among the sites of CSF withdrawal. The third ventricle contains the highest concentration of melatonin and the choroid plexus and the pituitary recess the lowest. All the melatonin concentrations in HIV-1 infection are largely different than in hydrocephalic controls. This is the first report on the measurement of tryptophan metabolites via serotonin in ventricular CSF in HIV-1 infection.

Study of tryptophan metabolism via serotonin in cerebrospinal fluid of patients with noncommunicating hydrocephalus using a new endoscopic technique.

By a recent minimally invasive neuroendoscopic technique, the cerebral ventricles have been reached in a quick, reliable, and harmless way, making possible the study of cerebrospinal fluid (CSF) of the lateral ventricles and, above all, the CSF adjacent to the walls of the third ventricle. Tryptophan, 5-hydroxytryptophan, serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were measured in CSF by HPLC equipment. Twenty-six patients affected with noncommunicating hydrocephalus were enrolled in the study and, as controls, 28 subjects not suffering from any neurological disease. The concentrations of tryptophan were higher in right ventricular CSF than in lumbar CSF (P < 0.01). 5-HT was detectable in the CSF of the right ventricle of hydrocephalic patients. 5-HIAA was higher in right ventricular CSF than in cisternal and lumbar CSF (P < 0.01), both in controls and in hydrocephalic patients. However, there was a higher concentration of 5-HIAA in right ventricular (P < 0.05) and cisternal (P < 0.01) CSF in hydrocephalic patients in comparison with controls. In the CSF samples withdrawn during neuroendoscopy, 5-HT presented the highest concentrations in the pineal recess. The highest amounts of 5-HIAA were found in the choroid plexus, third and right ventricles, pituitary recess, and aqueduct, and the lowest in pineal recess, subarachnoid space, infundibulum, and interpeduncolar cistern. These results provide new insight into the fate of tryptophan and its metabolites via serotonin in the CSF and suggest the feasibility of the new neuroendoscopic technique for brain metabolic studies.

A novel neurodevelopmental syndrome responsive to 5-hydroxytryptophan and carbidopa.

Tryptophan hydroxylase (TPH; EC 1.14.16.4) catalyzes the first rate-limiting step of serotonin biosynthesis by converting l-tryptophan to 5-hydroxytryptophan. Serotonin controls multiple vegetative functions and modulates sensory and alpha-motor neurons at the spinal level. We report on five boys with floppiness in infancy followed by motor delay, development of a hypotonic-ataxic syndrome, learning disability, and short attention span. Cerebrospinal fluid (CSF) analysis showed a 51 to 65% reduction of the serotonin end-metabolite 5-hydroxyindoleacetic acid (5HIAA) compared to age-matched median values. In one out of five patients a low CSF 5-methyltetrahydrofolate (MTHF) was present probably due to the common C677T heterozygous mutation of the methylenetetrahydrofolate reductase (MTHFR) gene. Baseline 24-h urinary excretion showed diminished 5HIAA values, not changing after a single oral load with l-tryptophan (50-70 mg/kg), but normalizing after 5-hydroxytryptophan administration (1 mg/kg). Treatment with 5-hydroxytryptophan (4-6 mg/kg) and carbidopa (0.5-1.0 mg/kg) resulted in clinical amelioration and normalization of 5HIAA levels in CSF and urine. In the patient with additional MTHFR heterozygosity, a heterozygous missense mutation within exon 6 (G529A) of the TPH gene caused an exchange of valine by isoleucine at codon 177 (V177I). This has been interpreted as a rare DNA variant because the pedigree analysis did not provide any genotype-phenotype correlation. In the other four patients the TPH gene analysis was normal. In conclusion, this new neurodevelopmental syndrome responsive to treatment with 5-hydroxytryptophan and carbidopa might result from an overall reduced capacity of serotonin production due to a TPH gene regulatory defect, unknown factors inactivating the TPH enzyme, or selective loss of serotonergic neurons.

Influence of repeated levodopa administration on rabbit striatal serotonin metabolism, and comparison between striatal and CSF alterations.

Parkinson's disease (PD) is characterized by decreased striatal dopamine, but serotonin (5-HT) is also reduced. Because 5-HT decreases following a single levodopa injection, levodopa has been suggested to contribute to PD's serotonergic deficits. However, in a recent study, rat striatal serotonin levels were reported to increase following 15-day levodopa administration. To address this issue, we administered levodopa (50 mg/kg) to rabbits for 5 days, then measured serotonin, its precursors tryptophan and 5-hydroxytryptophan (5-HTP), and its major metabolite 5-hydroxyindole-acetic acid (5-HIAA) in striatum and CSF. Striatal serotonin and tryptophan were unchanged, while 5-HTP and 5-HIAA increased 4- and 7-fold, respectively. CSF 5-HTP and 5-HIAA were also significantly increased. In levodopa-treated animals, 5-HTP concentrations were moderately correlated (r = 0.679) between striatum and CSF, while weak correlations were present between striatal and CSF concentrations of both serotonin and 5-HIAA. These results suggest that repeated levodopa treatment increases striatal serotonin turnover without changing serotonin content. However, levodopa-induced alterations in striatal serotonin metabolism may not be accurately reflected by measurement of serotonin and 5-HIAA in CSF.

Concentrations of indoleamine metabolic intermediates in the ventricular cerebrospinal fluid of advanced Parkinson's patients with severe postural instability and gait disorders.

Postural instability and gait disorders (PIGD) are the primary causes of disability in many but not all advanced Parkinson's disease (PD) patients. We have measured the concentrations of serotonin, 5-hydroxytryptophan (5-HTP), 5-hydroxy-3-indoleacetic acid (5-HIAA), and homovanillic acid (HVA) in samples of ventricular cerebrospinal fluid from ten PD patients with severe disability from PIGD and from ten PD patients with tremor and levodopa induced dyskinesia as their predominant motor dysfunction. The two groups were prospectively matched for duration of disease and age. No significant differences between the two groups were found in the concentration (mean +/- SD in ng/ml, PIGD dominant vs. tremor-dyskinesia dominant) of 5-HIAA (106 +/- 50 vs. 99 +/- 34) or HVA (1,068 +/- 595 vs. 881 +/- 469). Serotonin concentration was significantly lower (0.7 +/- 0.5 vs. 1.5 +/- 0.9) and 5-HTP concentration was substantially higher (684 +/- 1,054 vs. 6 +/- 5) in the patient group with PIGD as their predominant symptoms. Thus, the distinguishing feature of patients with severe PIGD appears to be a derangement in indoleamine metabolism at the reaction step catalyzed by aromatic amino acid decarboxylase (AADC). These findings suggest that aggravation of PIGD in advanced Parkinson's may be related in part to impaired serotonergic transmission secondary to inhibition or down regulation of AADC.

Simultaneous determination of tryptophan, 5-hydroxytryptophan, 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, 4-hydroxy-3-methoxyphenylacetic acid and 3-methoxy-4-hydroxyphenylglycol in human cerebrospinal fluid.

Serotonin (5-hydroxytryptamine) metabolism may be influenced by its precursor tryptophan. A method utilizing reversed-phase high-performance liquid chromatography and electrochemical and ultraviolet detection with a mobile phase composed of acetate buffer and methanol has been developed for determination of tryptophan, its metabolites 5-hydroxytryptophan, serotonin, 5-hydroxyindoleacetic acid, as well as 4-hydroxy-3-methoxyphenylacetic acid (homovanillic acid) and 3-methoxy-4-hydroxyphenylglycol in human cerebrospinal fluid (CSF). The electrochemical potential is set at 0.6 V in order to reduce the background current. Since tryptophan is not electroactive at this potential, it is detected by ultraviolet absorbance. The present method is simple, rapid, specific and accurate as compared with a previously reported method. No sample pretreatment is necessary and it takes ca. 20 min to run a sample. The concentrations of the compounds measured in CSF are similar to those obtained by HPLC in previous reports, although there are still arguments about the true level of serotonin in CSF.

Changes in serotonin metabolism may elicit obstructive apnoea in the newborn rat.

1. Experiments were performed on anaesthetized newborn rats (aged 3-10 days) to know whether an increase in central serotonin levels might favour the occurrence of obstructive apnoeas as previously suggested by in vitro results from our group. 2. The levels of serotonin (5-HT), its precursor 5-hydroxytryptophan (5-HTP) and its metabolite, 5-hydroxyindole-acetic acid (5-HIAA), were analysed in cerebrospinal fluid samples collected at the level of the obex prior to and after intraperitoneal injection of L-tryptophan (50 mg kg-1) in sixty-eight anaesthetized newborn rats (control rats prior to injection and injected rats 15, 30 and 45 min after the injection). A significant increase in 5-HT and 5-HTP levels occurred 30 min after the injection, attesting to the activation of 5-HT biosynthesis. 3. The EMG activity of both the genioglossus and the diaphragm was recorded before and after L-tryptophan load (50 mg kg-1) in twenty-two newborn rats. After the injection of L-tryptophan, the amplitude of the integrated genioglossus activity decreased, or was even abolished, either during a few respiratory cycles or for long periods in twenty-one out of twenty-two animals. Recovery of the genioglossus activity occurred within 45-60 min. 4. The thoracic respiratory movements and the resulting upper airway pressure changes were recorded before and after L-tryptophan injection (50 mg kg-1) in sixty-two animals. In some litters (n = 7), most of the animals (21/25) displayed, within 20-40 min of the injection, recurrent episodes of obstructive apnoea often followed by central ones. These respiratory difficulties became severe and drastic, and led in two instances to respiratory distress and death. Lower doses of L-tryptophan (10 mg kg-1) did not induce any respiratory disorders unless these were potentiated by pargyline treatment (50 mg kg-1, n = 7). The obstructive apnoeas liable to occur after an L-tryptophan load (50 mg kg-1) were prevented by blocking the 5-HT receptor with methysergide (50 mg kg-1, n = 5) or by blocking the 5-HT biosynthesis by applying p-chlorophenylalanine (PCPA) pretreatment at birth (300 mg kg-1, n = 7). In other litters (n = 6), none of the eighteen newborn rats tested were affected by L-tryptophan, however, In five young adult rats, L-tryptophan again had no effect.4+ e

Concentrations of serotonin and its related substances in the cerebrospinal fluid of parkinsonian patients and their relations to the severity of symptoms.

We evaluated the concentrations of free and total serotonin (5-hydroxytryptamine, 5-HT) and its related substances in the cerebrospinal fluid from patients with Parkinson's disease (PD). The concentrations of total 5-HT, 5-hydroxytryptophan, kynurenine and 3-hydroxykynurenine decreased significantly in PD patients compared with controls. The concentration of total 5-HT had significant negative correlations with Hoehn and Yahr's stages, the severity of rigidity, akinesia and gait freezing; the correlation with gait freezing was most conspicuous.

Aromatic L-amino acid decarboxylase deficiency: diagnostic methodology.

Aromatic L-amino acid decarboxylase (EC. 4.1.1.28) deficiency is a newly described inborn error of metabolism that affects serotonin and dopamine biosynthesis. The major biochemical markers for this disease are increases of L-dopa, 3-methoxytyrosine, and 5-hydroxytryptophan in urine, plasma, and cerebrospinal fluid together with decreased cerebrospinal fluid concentrations of homovanillic acid and 5-hydroxyindoleacetic acid. In addition, concentrations of vanillactic acid are increased in the urine. Specific HPLC and gas chromatography-mass spectrometry methods are described that permit the identification and measurement of these metabolites in the above body fluids. Simplified assays for human plasma L-dopa decarboxylase and liver L-dopa and 5-hydroxytryptophan decarboxylase, used to demonstrate the enzyme deficiency, are also reported.

Studies on CSF tryptophan metabolism in infantile spasms.

Cerebrospinal fluid from 8 patients with infantile spasms (mean age: 6.1 months) was collected before treatment. The concentration of cerebrospinal fluid tryptophan metabolites was analyzed using high-performance liquid chromatography and compared to metabolite concentrations in cerebrospinal fluid from 20 age-matched controls (mean age: 5.8 months). The levels of cerebrospinal fluid serotonin, 5-hydroxyindoleacetic acid, and kynurenine were significantly lower in infantile spasm patients compared to controls (P less than .05). In contrast, the levels of cerebrospinal fluid 3-hydroxykynurenine were significantly higher in infantile spasm patients than in controls (P less than .05). There were no significant differences in the levels of cerebrospinal fluid tryptophan and 5-hydroxytryptophan. Although the study population was small, these findings suggest that the presence of seizures in infantile spasms is associated with a decrease in serotonergic metabolites which, in turn, may indicate a decrease in serotonergic activity, altered clearance of these metabolites, or altered turnover in the direction of 3-hydroxykynurenine. The perturbance caused by increased 3-hydroxykynurenine and decreased kynurenine in the homeostatic balance between these 2 tryptophan metabolites could further contribute to the pathogenesis of infantile spasms.

The effects of ammonia tolerance tests on the cerebrospinal fluid concentrations of amino acids and indoleamines in patients with liver cirrhosis.

To study the effect of ammonia administration on amino acids and indoleamines in cerebrospinal fluid (CSF) and on amino acids, insulin, and glucagon in plasma in humans with liver cirrhosis, we performed seven ammonia tolerance tests on six patients with stable liver cirrhosis. The grade of encephalopathy was determined by psychometric tests. Only one of the patients had pronounced encephalopathy. The other patients had no or only slight encephalopathy. The plasma concentrations of valine, leucine, isoleucine, phenylalanine, tyrosine, and methionine decreased after the ammonia load, whereas no changes were found in the plasma concentrations of glucagon and insulin. In CSF the concentrations of glutamine, aromatic amino acids, and indoleamines increased only in the patient who had pronounced encephalopathy, whereas no changes were found in the other patients. The effect of an ammonia load on the concentrations of neutral amino acids in CSF in patients with pronounced encephalopathy remains to be demonstrated.

Tryptophan, 5-HTP, 5-HT and 5-HIAA in the cerebrospinal fluid and sexual behavior in male rats.

No changes were found in the concentration of tryptophan (Trp), 5-hydroxytryptophan (5-HTP), 5-hydroxytryptamine (5-HT) or 5-hydroxyindole acetic acid (5-HIAA) in the cerebrospinal fluid (CSF) of male rats either before sexual activity, immediately after ejaculation of after the postejaculatory refractory period (PEI). Injection of the Trp hydroxylase inhibitor p-chlorophenylalanine (PCPA, 25 or 100 mg/kg i.p. for 3 days) in combination with an injection of the monoamine oxidase inhibitor pargyline (100 mg/kg i.p.) increased the concentration of Trp while decreasing the concentration of 5-HTP, 5-HT and 5-HIAA in the CSF. Furthermore 100 (but not 25) mg/kg PCPA in combination with pargyline caused a significant reduction in the latency to ejaculation. Injection of probenecid (200 mg/kg i.p.), an inhibitor of the transport of 5-HIAA from the CSF, increased the concentration of 5-HIAA in the CSF and slightly prolonged the latency to ejaculation. Sexual activity caused no further increase in CSF 5-HIAA levels in the probenecid-treated rats. Since drug-induced changes in sexual behavior are associated with marked alterations in 5-HT metabolism in the CSF, whereas the changes in the behavior which occur normally are not, these results question the physiological significance of the proposed inhibitory role of 5-HT in male rat sexual behavior.

Clinical, biochemical, and pharmacological observation in a patient with postasphyxic myoclonus: association to serotonin hyperactivity.

Posthypoxic action myoclonus is usually associated with impaired serotonin (5-HT) neurotransmission but in some patients 5-HT precursors aggravate and 5-HT blockers improve action myoclonus. We studied a 65-year-old man who presented with action myoclonus following a prolonged episode of moderate hypoxia and severe hypercarbia. The myoclonus increased with 5-hydroxytryptophan (5-HTP) 1,200 mg/day plus carbidopa 300 mg/day and sodium salt of valproic acid (SVA) 800 mg/day, and improved with 1 mg of clonazepam (CNZ) in an intravenous bolus. Biochemical analysis of the cerebrospinal fluid (CSF) prior to any drug therapy did not reveal abnormalities in the levels of homovanillic acid (HVA) and methoxyhydroxyphenylglycol (MHPG) but 5-hydroxyindoleacetic acid (5-HIAA) levels were elevated in comparison with controls (33 versus 21 ng/ml). SVA therapy produced a moderate increase and 5-HTP plus carbidopa a threefold elevation of 5-HIAA in CSF and marked aggravation of action myoclonus. Methysergide (3 mg/day) totally suppressed myoclonus and decreased CSF 5-HIAA to undetectable levels. Methysergide also reduced CSF tryptophan to 40% of baseline levels. Discontinuation of methysergide and substitution by placebo was followed by reappearance of myoclonus. A partial and incomplete spontaneous remission of symptoms took place 7 months after the asphyxic episode. Action myoclonus and enhanced 5-HT neurotransmission may be present in patients in which acidosis reverses the effects of hypoxia on 5-HT neurotransmission.

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.

Indole levels in human lumbar and ventricular cerebrospinal fluid and the effect of L-tryptophan administration.

Levels of tryptophan (TRP), 5-hydroxytryptophan (5-HTP), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in human lumbar and ventricular cerebrospinal fluid (CSF) were measured by reversed phase liquid chromatography (HPLC) with electrochemical detection. The levels of TRP ranged from 1593 to 4865 nmol/l in ventricular (VF) and from 1257 to 2557 nmol/l in lumbar CSF. The level of 5-HTP varied from 1.1 to 68.9 nmol/l in VF and from 5.3 to 10.8 nmol/l in lumbar CSF; no previous reports of 5-HTP levels in CSF exist. The serotonin level was 1.9-27.3 nmol/l in VF and 5.7-12.0 nmol/l in lumbar CSF. The levels of 5-HIAA were considerably higher in VF than in lumbar fluid with respective means of 498 +/- 52.4 nmol/l and 112 +/- 15.6 nmol/l (P less than 0.001). An oral dose of 2 g L-tryptophan significantly increased all indole levels except that of 5-HT, both in patients with progressive myoclonus epilepsy and in controls.

n-Electrode three-dimensional liquid chromatography with electrochemical detection for determination of neurotransmitters.

Coulometric electrodes in series have been used with liquid chromatography with electrochemical detection to increase selectivity and resolution for the direct analysis of tissue neurotransmitters. Use of three coulometric sensors for electrochemical modification, selectivity, and peak identification has been expanded into "gate" cells of three or four coulometric electrodes that allow elimination of all electrochemically irreversible substances, and "array" cells of up to 15 coulometric electrodes for separation of co-eluting compounds by their current/voltage characteristics. On-column sensitivity of the sensor arrays is 0.4 to 4 pg. Gate cell selectivity favors electrochemically reversible compounds over irreversible ones, e.g., 3-methoxy-4-hydroxyphenylglycol vs ascorbate, by a factor of up to 10(4). Resolution across the multi-electrode array cells allows separation of co-eluting compounds with half-wave potentials differing by as little as 30 to 40 mV. Cells with three to 15 electrodes have been used to measure monoamines and metabolites in brain; monoamines directly in serum filtrate; and the state of oxidation of 5-hydroxytryptamine and 5-hydroxytryptophan in cerebrospinal fluid of patients with Alzheimer's disease.